mlx5: Pass the correct data pointer to the add_dst_cb instead of NULL.

Reported by:	-Wunused-but-set-variable
Reviewed by:	hselasky
Differential Revision:	https://reviews.freebsd.org/D34812

sys/dev/mlx5/mlx5_core/mlx5_fs_tree.c

@@ -1521,7 +1521,7 @@ static void call_to_add_rule_notifiers(struct mlx5_flow_rule *dst,
 			mutex_unlock(&dst->clients_lock);
 			err  = iter_handler->add_dst_cb(dst,
 							is_new_rule,
-							NULL,
+							data,
 							iter_handler->client_context);
 			if (err)
 				break;