drivers/macintosh/adb: Do not claim that the semaphore is a mutex

User DEFINE_SEMAPHORE() instead of DECLARE_MUTEX()

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
LKML-Reference: <20100907125057.086367802@linutronix.de>