[media] lmedm04: Do not unlock mutex if mutex_lock_interruptible failed

There are a couple of places where mutex_unlock() is called even
if mutex_lock_interruptible() failed. The patch fixes the issue.

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>