NFS41/flexfiles: update inode after write finishes

Otherwise we break fstest case tests/read_write/mctime.t

Does files layout need the same fix as well?

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

fs/nfs/flexfilelayout/flexfilelayout.c

@@ -1199,6 +1199,9 @@ static int ff_layout_write_done_cb(struct rpc_task *task,
 	    hdr->res.verf->committed == NFS_DATA_SYNC)
 		ff_layout_set_layoutcommit(hdr);
 
+	if (task->tk_status >= 0)
+		nfs_writeback_update_inode(hdr);
+
 	return 0;
 }