[media] rc-core: fix remove uevent generation

The input_dev is already gone when the rc device is being unregistered
so checking for its presence only means that no remove uevent will be
generated.

Cc: stable@kernel.org
Signed-off-by: David Härdeman <david@hardeman.nu>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>