stasis: fix call to ao2_t_alloc for stasis_message_router_create

This fixes a build failure introduced by r3821.  struct stasis_topic is
opaque, so topic->name is unavailable.  Switch to using stasis_topic_name().
........

Merged revisions 419019 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@419020 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/stasis_message_router.c

@@ -212,7 +212,7 @@ struct stasis_message_router *stasis_message_router_create(
 	int res;
 	RAII_VAR(struct stasis_message_router *, router, NULL, ao2_cleanup);
 
-	router = ao2_t_alloc(sizeof(*router), router_dtor, topic->name);
+	router = ao2_t_alloc(sizeof(*router), router_dtor, stasis_topic_name(topic));
 	if (!router) {
 		return NULL;
 	}