affs: Use sema_init instead of init_MUTEX

Get rid of init_MUTE() and use sema_init() instead.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
LKML-Reference: <20100907125056.511395595@linutronix.de>