rc-core: fix remove uevent generation

commit a66b0c41ad277ae62a3ae6ac430a71882f899557 upstream.

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.

Signed-off-by: David Härdeman <david@hardeman.nu>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>