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/flow.c b/flow.c
index bf5eeec..2993f4e 100644
--- a/flow.c
+++ b/flow.c
@@ -92,7 +92,7 @@
 
 void flow_init(void)
 {
-	flow_lock = fio_mutex_init(1);
+	flow_lock = fio_mutex_init(FIO_MUTEX_UNLOCKED);
 	flow_list = smalloc(sizeof(*flow_list));
 	INIT_FLIST_HEAD(flow_list);
 }