Add rw mutex init helper

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/mutex.h b/mutex.h
index 7451593..40cfc1e 100644
--- a/mutex.h
+++ b/mutex.h
@@ -20,4 +20,9 @@
 extern void fio_mutex_up_read(struct fio_mutex *);
 extern void fio_mutex_up_write(struct fio_mutex *);
 
+static inline struct fio_mutex *fio_mutex_rw_init(void)
+{
+	return fio_mutex_init(0);
+}
+
 #endif