Use mutexes instead of semaphores in I2O driver

The I2O driver uses two semaphores as mutexes.  Use the mutex API instead of
the (binary) semaphores.

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