detect/port: workaround cppcheck warning

src/detect-engine-port.c

@@ -1059,7 +1059,8 @@ int DetectPortTestConfVars(void)
 {
     SCLogDebug("Testing port conf vars for any misconfigured values");
 
-    ResolvedVariablesList var_list = TAILQ_HEAD_INITIALIZER(var_list);
+    ResolvedVariablesList var_list;
+    TAILQ_INIT(&var_list);
 
     SCConfNode *port_vars_node = SCConfGetNode("vars.port-groups");
     if (port_vars_node == NULL) {