rxrpc: checking for IS_ERR() instead of NULL

The rxrpc_lookup_peer() function returns NULL on error, it never returns
error pointers.

Fixes: 8496af50 ('rxrpc: Use RCU to access a peer's service connection tree')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/rxrpc/conn_service.c

@@ -163,7 +163,7 @@ struct rxrpc_connection *rxrpc_incoming_connection(struct rxrpc_local *local,
 
 	if (!peer) {
 		peer = rxrpc_lookup_peer(local, srx, GFP_NOIO);
-		if (IS_ERR(peer))
+		if (!peer)
 			goto enomem;
 	}