domain: fix compilation warnings for kemi updates

src/modules/domain/domain.c

@@ -202,7 +202,7 @@ int ki_lookup_domain_prefix(struct sip_msg *_msg, str *_sdomain, str *_sprefix)
 {
 	int_str name, val;
 	struct attr_list *attrs;
-	str *prefix, did;
+	str did;
 	unsigned short flags;
 
 	if(_sdomain==NULL || _sdomain->s==NULL) {
@@ -517,4 +517,4 @@ err:
 	res = NULL;
 	domain_db_close();
 	return -1;
-}
+}