drivers/edac: change from semaphore to mutex operation

The EDAC core code uses a semaphore as mutex. use the mutex API
instead of the (binary) semaphore.

Matthaias wrote this, but since I had some patches ahead of it,
I need to modify it to follow my patches.

Signed-off-by: Matthias Kaehlcke <matthias.kaehlcke@gmail.com>
Signed-off-by: Douglas Thompson <dougthompson@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>