PNFS fallback to MDS if no deviceid found

If we fail to find a good deviceid while trying to pnfs instead of
propogating an error back fallback to doing IO to the MDS. Currently,
code with fals the IO with EINVAL.
Signed-off-by: NOlga Kornievskaia <kolga@netapp.com>
Fixes: 8d40b0f1 ("NFS filelayout:call GETDEVICEINFO after pnfs_layout_process completes"
Cc: stable@vger.kernel.org # v4.11+
Signed-off-by: NAnna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/filelayout/filelayout.c

@@ -904,7 +904,7 @@ fl_pnfs_update_layout(struct inode *ino,
 	status = filelayout_check_deviceid(lo, fl, gfp_flags);
 	if (status) {
 		pnfs_put_lseg(lseg);
-		lseg = ERR_PTR(status);
+		lseg = NULL;
 	}
 out:
 	return lseg;