[ARM] OMAP1: N770: Convert audio_pwr_sem in a mutex

ARM: OMAP1: N770: The semaphore audio_pwr_sem is used as a
mutex. Convert it to the mutex API

[akpm@linux-foundation.org: include mutex.h]
Signed-off-by: Matthias Kaehlcke <matthias@kaehlcke.net>
Cc: Tony Lindgren <tony@atomide.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>