[SPARC] Videopix Frame Grabber: Convert device_lock_sem to mutex

Videopix Frame Grabber: Convert the semaphore device_lock_sem to the
mutex API

Signed-off-by: Matthias Kaehlcke <matthias.kaehlcke@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>