NFS41/flexfiles: zero out DS write wcc

We do not want to update inode attributes with DS values.

Cc: stable@vger.kernel.org # v4.0+
Signed-off-by: NPeng Tao <tao.peng@primarydata.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/flexfilelayout/flexfilelayout.c

@@ -1218,6 +1218,8 @@ static int ff_layout_write_done_cb(struct rpc_task *task,
 	    hdr->res.verf->committed == NFS_DATA_SYNC)
 		ff_layout_set_layoutcommit(hdr);
 
+	/* zero out fattr since we don't care DS attr at all */
+	hdr->fattr.valid = 0;
 	if (task->tk_status >= 0)
 		nfs_writeback_update_inode(hdr);