[media] dib9000: release a lock on error

This lock should be released as well on the error path.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Patrick Boettcher <Patrick.Boettcher@dibcom.fr>
Cc: Olivier Grenie <olivier.grenie@dibcom.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>