[media] dib9000: implement error handling for DibAcquireLock

DibAcquireLock() is implemented as mutex_lock_interruptible()
but the driver does not handle unsuccessful locking.
As a result it may lead to unlock of an unheld mutex.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>