mutex: make 0/1 FIO_MUTEX_LOCKED and FIO_MUTEX_UNLOCKED

Makes the API look cleaner.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/cgroup.c b/cgroup.c
index ea6bbd6..86d4d5e 100644
--- a/cgroup.c
+++ b/cgroup.c
@@ -182,7 +182,7 @@
 
 static void fio_init cgroup_init(void)
 {
-	lock = fio_mutex_init(1);
+	lock = fio_mutex_init(FIO_MUTEX_UNLOCKED);
 }
 
 static void fio_exit cgroup_exit(void)