flist: add flist_first_entry()

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/io_u.c b/io_u.c
index 5b9d483..16b52d6 100644
--- a/io_u.c
+++ b/io_u.c
@@ -223,7 +223,7 @@
 	if (!flist_empty(&td->next_rand_list)) {
 		struct rand_off *r;
 fetch:
-		r = flist_entry(td->next_rand_list.next, struct rand_off, list);
+		r = flist_first_entry(&td->next_rand_list, struct rand_off, list);
 		flist_del(&r->list);
 		*b = r->off;
 		free(r);