Input: synaptics-rmi4 - destroy F54 poller workqueue when removing

The driver forgets to destroy workqueue in remove() similarly to what is
done when probe() fails. Add a call to destroy_workqueue() to fix it.

Since unregistration will wait for the work to finish, we do not need to
cancel/flush the work instance in remove().

Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20191114023405.31477-1-hslester96@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/rmi4/rmi_f54.c

@@ -730,6 +730,7 @@ static void rmi_f54_remove(struct rmi_function *fn)
 
 	video_unregister_device(&f54->vdev);
 	v4l2_device_unregister(&f54->v4l2);
+	destroy_workqueue(f54->workqueue);
 }
 
 struct rmi_function_handler rmi_f54_handler = {