scx200_acb: Use mutex instead of semaphore

The scx200_acb driver use a semaphore as mutex.  Use the mutex API
instead of the (binary) semaphore.

Signed-off-by: Matthias Kaehlcke <matthias.kaehlcke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Jordan Crouse <jordan.crouse@amd.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>