[RXRPC] net/rxrpc/ar-connection.c: fix NULL dereference

This patch fixes a NULL dereference spotted by the Coverity checker.
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/rxrpc/ar-connection.c

@@ -211,7 +211,7 @@ static struct rxrpc_connection *rxrpc_alloc_connection(gfp_t gfp)
 		conn->header_size = sizeof(struct rxrpc_header);
 	}
 
-	_leave(" = %p{%d}", conn, conn->debug_id);
+	_leave(" = %p{%d}", conn, conn ? conn->debug_id : 0);
 	return conn;
 }