nfs41: free the slot on unhandled read errors

nfs4_read_done returns zero on unhandled errors. nfs_readpage_result will
return on a negative tk_status without freeing the slot.
Call nfs4_sequence_free_slot on unhandled errors in nfs4_read_done.
Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4proc.c

@@ -3009,6 +3009,9 @@ static int nfs4_read_done(struct rpc_task *task, struct nfs_read_data *data)
 	nfs_invalidate_atime(data->inode);
 	if (task->tk_status > 0)
 		renew_lease(server, data->timestamp);
+	else if (task->tk_status < 0)
+		nfs4_sequence_free_slot(server->nfs_client, &data->res.seq_res);
+
 	return 0;
 }