mirror: Replace bdrv_drain(bs) with bdrv_co_drain(bs)

Suggested-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NFam Zheng <famz@redhat.com>
Message-id: 1459855253-5378-3-git-send-email-famz@redhat.com
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

block/mirror.c

@@ -650,7 +650,7 @@ static void coroutine_fn mirror_run(void *opaque)
              * mirror_populate runs.
              */
             trace_mirror_before_drain(s, cnt);
-            bdrv_drain(bs);
+            bdrv_co_drain(bs);
             cnt = bdrv_get_dirty_count(s->dirty_bitmap);
         }