media: rc: oops in ir_timer_keyup after device unplug

If there is IR in the raw kfifo when ir_raw_event_unregister() is called,
then kthread_stop() causes ir_raw_event_thread to be scheduled, decode
some scancodes and re-arm timer_keyup. The timer_keyup then fires when
the rc device is long gone.

Cc: stable@vger.kernel.org
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>