tls_mgm: fix variable name from previous commit

(cherry picked from commit 008196a)

modules/tls_mgm/tls_domain.c

@@ -117,7 +117,7 @@ void tls_free_domain(struct tls_domain *dom)
 	dom->refs--;
 	if (dom->refs == 0) {
 		LM_DBG("Freeing domain: %.*s\n",
-			tls_domain->name.len, tls_domain->name.s);
+			dom->name.len, dom->name.s);
 
 		destroy_tls_dom(dom);