md: remove md_super_wait() call after bitmap_flush()

bitmap_flush() finishes with bitmap_update_sb(), and that finishes
with write_page(..., 1), so write_page() will wait for all writes
to complete.  So there is no point calling md_super_wait()
immediately afterwards.
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

drivers/md/md.c

@@ -5472,7 +5472,6 @@ static void __md_stop_writes(struct mddev *mddev)
 	del_timer_sync(&mddev->safemode_timer);
 
 	bitmap_flush(mddev);
-	md_super_wait(mddev);
 
 	if (mddev->ro == 0 &&
 	    ((!mddev->in_sync && !mddev_is_clustered(mddev)) ||