V4L/DVB: IR/mceusb: use the proper ir-core device unregister function

Was using input_unregister_device directly, instead of using
ir_input_unregister, which tears down a bunch of other things in
addition to eventually calling input_unregister_device.

Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>