[SCSI] osst: Use mutex instead of semaphore

The OnStream SCSI Tape driver uses a semaphore as mutex.  Use the mutex API
instead of the (binary) semaphore.

Signed-off-by: Matthias Kaehlcke <matthias.kaehlcke@gmail.com>
Reviewed-by: Satyam Sharma <satyam@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Willem Riede <wrlk@riede.org>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>