Seems copied from sysfs, but I don't see a reason here nor there to use
a semaphore instead of a mutex. Convert.
Signed-off-by: NJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: NJoel Becker <joel.becker@oracle.com>
Signed-off-by: NMark Fasheh <mark.fasheh@oracle.com>