media: rc: do not access device via sysfs after rc_unregister_device()

Device drivers do not expect to have change_protocol or wakeup
re-programming to be accesed after rc_unregister_device(). This can
cause the device driver to access deallocated resources.

Cc: <stable@vger.kernel.org> # 4.16+
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>