[IA64-SGI] sem2mutex ioc4.c

Convert to use a single mutex instead of two rwsems as this isn't
performance critical.

Signed-off-by: Jes Sorensen <jes@sgi.com>
Signed-off-by: Brent Casavant <bcasavan@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>