We don't write back stale inodes so we should skip them in
xfs_iflush_cluster, too.

cc: <stable@vger.kernel.org> # 3.10.x-
Signed-off-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NDave Chinner <david@fromorbit.com>