[media] dvb-core: Release semaphore on error path dvb_register_device()

There is a missing "up_write()" here. Semaphore should be released
before returning error value.

Cc: stable@kernel.org
Signed-off-by: Santosh Nayak <santoshprasadnayak@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>