adjust to vmod_priv methods

Ref:
https://github.com/varnishcache/varnish-cache/commit/681c11998ec56dc4460a30585210f95a7850ea3b

src/vmod_selector.c

@@ -437,7 +437,7 @@ get_match_data(VRT_CTX, struct vmod_selector_set *set, const char *method)
 			return (NULL);
 		}
 		task->len = sizeof(*match);
-		task->free = NULL;
+		AZ(task->methods);
 		match = (struct match_data *)task->priv;
 		match->magic = MATCH_DATA_MAGIC;
 	}