ev3_ports_in: fix trying to cancel uninitalized work

__flush_work() has been modifed to warn when called with
an unintialed work struct. So, we need to protect against
calling it when we have not initalized data->work.

Fixes the following warning:

[43297.092951] ------------[ cut here ]------------
[43297.098131] WARNING: CPU: 0 PID: 667 at /home/david/work/ev3dev-dpkg/ev3dev-kpkg/ev3-kernel/kernel/workqueue.c:2911 __flush_work+0x74/0x218
[43297.113331] Modules linked in: iptable_nat nf_nat_ipv4 nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 libcrc32c usb_f_rndis usb_f_ecm u_ether ev3_uart_sensor_ld ev3_uart_sensor rtl8150 hci_uart nxt_i2c_sensor servo_motor_class uinput libcomposite sunrpc ip_tables x_tables
[43297.140457] CPU: 0 PID: 667 Comm: bash Not tainted 4.19.85-ev3dev-3-beta1-ev3+ #502
[43297.148915] Hardware name: LEGO MINDSTORMS EV3
[43297.156605] Backtrace:
[43297.158370] [<c000d7ec>] (dump_backtrace) from [<c000daa8>] (show_stack+0x18/0x1c)
[43297.166133]  r7:00000009 r6:00000000 r5:c06b2c50 r4:00000000
[43297.181258] [<c000da90>] (show_stack) from [<c0558bd8>] (dump_stack+0x20/0x28)
[43297.198079] [<c0558bb8>] (dump_stack) from [<c0018ffc>] (__warn+0xe8/0x104)
[43297.224279] [<c0018f14>] (__warn) from [<c0019134>] (warn_slowpath_null+0x44/0x50)
[43297.235383]  r9:c002e9d8 r8:ffffe000 r7:00000000 r6:c002e208 r5:00000b5f r4:c06b2c50
[43297.249291] [<c00190f0>] (warn_slowpath_null) from [<c002e208>] (__flush_work+0x74/0x218)
[43297.258805]  r6:c3b8d22c r5:c0771008 r4:00000000
[43297.263365] [<c002e194>] (__flush_work) from [<c0030b80>] (__cancel_work_timer+0x128/0x1c4)
[43297.276470]  r8:ffffe000 r7:00000000 r6:c0771008 r5:c3b8d22c r4:ffffffe0
[43297.295256] [<c0030a58>] (__cancel_work_timer) from [<c0030c30>] (cancel_work_sync+0x14/0x18)
[43297.313222]  r9:00000051 r8:00000033 r7:00000008 r6:c3b8d240 r5:c3b8d22c r4:c3b8d020
[43297.329277] [<c0030c1c>] (cancel_work_sync) from [<c03e72b8>] (ev3_input_port_set_mode+0x30/0x1b8)
[43297.358626] [<c03e7288>] (ev3_input_port_set_mode) from [<c03e4f10>] (mode_store+0x70/0xa4)
[43297.372683]  r7:00000004 r6:00000008 r5:00000008 r4:c3b8d090
[43297.383258] [<c03e4ea0>] (mode_store) from [<c02e7ce8>] (dev_attr_store+0x20/0x2c)
[43297.399219]  r9:00000051 r8:c3959bb0 r7:c3159f60 r6:c3959ba0 r5:c30dc900 r4:c03e4ea0
[43297.412968] [<c02e7cc8>] (dev_attr_store) from [<c014b318>] (sysfs_kf_write+0x40/0x4c)
[43297.438883]  r5:c30dc900 r4:c02e7cc8
[43297.453229] [<c014b2d8>] (sysfs_kf_write) from [<c014a638>] (kernfs_fop_write+0x138/0x1a8)
[43297.483787]  r5:c30dc900 r4:00000004
[43297.490029] [<c014a500>] (kernfs_fop_write) from [<c00da6dc>] (__vfs_write+0x40/0x164)
[43297.503387]  r9:00000004 r8:c3159f60 r7:c0771008 r6:00125a08 r5:c33ad6e0 r4:c014a500
[43297.511534] [<c00da69c>] (__vfs_write) from [<c00da9c0>] (vfs_write+0xc4/0x150)
[43297.524075]  r9:00000004 r8:00000000 r7:c3159f60 r6:00125a08 r5:00000004 r4:c33ad6e0
[43297.537895] [<c00da8fc>] (vfs_write) from [<c00dabf0>] (ksys_write+0x64/0xc0)
[43297.561845]  r9:00000004 r8:00125a08 r7:c0771008 r6:c33ad6e0 r5:00125a08 r4:c33ad6e0
[43297.588358] [<c00dab8c>] (ksys_write) from [<c00dac5c>] (sys_write+0x10/0x14)
[43297.608179]  r9:c3158000 r8:c00091e4 r7:00000004 r6:b6edbd50 r5:00125a08 r4:00000004
[43297.621605] [<c00dac4c>] (sys_write) from [<c0009000>] (ret_fast_syscall+0x0/0x50)
[43297.631751] Exception stack(0xc3159fa8 to 0xc3159ff0)
[43297.641204] 9fa0:                   00000004 00125a08 00000001 00125a08 00000004 00000000
[43297.659828] 9fc0: 00000004 00125a08 b6edbd50 00000004 00000004 00000004 00000000 00118fd8
[43297.670180] 9fe0: 00000000 bee8384c b6e0060c b6e5c04c
[43297.680830] ---[ end trace 8a3544246704cce4 ]---

Author: dlech

ev3/ev3_ports_in.c

@@ -929,7 +929,8 @@ static int ev3_input_port_set_mode(void *context, u8 mode)
 	 */
 
 	hrtimer_cancel(&data->timer);
-	cancel_work_sync(&data->work);
+	if (data->work.func)
+		cancel_work_sync(&data->work);
 
 	switch (data->port.mode) {
 	case EV3_INPUT_PORT_MODE_OTHER_I2C:
@@ -1259,7 +1260,8 @@ static int ev3_input_port_remove(struct platform_device *pdev)
 
 	hrtimer_cancel(&data->timer);
 	cancel_work_sync(&data->change_uevent_work);
-	cancel_work_sync(&data->work);
+	if (data->work.func)
+		cancel_work_sync(&data->work);
 	if (data->port.mode == EV3_INPUT_PORT_MODE_OTHER_UART)
 		ev3_input_port_disable_uart(data);
 	if (data->port.mode == EV3_INPUT_PORT_MODE_RAW)