The power management semaphore is only used as mutex, so convert it.

[akpm@osdl.org: fix rotten bug]
Signed-off-by: NStephen Hemminger <shemminger@osdl.org>
Acked-by: NIngo Molnar <mingo@elte.hu>
Acked-by: NPavel Machek <pavel@ucw.cz>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>