chore(examples): fix unused-variable warning (#3732)

Co-authored-by: pengyiqiang <pengyiqiang@xiaomi.com>

examples/widgets/switch/lv_example_switch_1.c

@@ -5,6 +5,7 @@ static void event_handler(lv_event_t * e)
 {
     lv_event_code_t code = lv_event_get_code(e);
     lv_obj_t * obj = lv_event_get_target(e);
+    LV_UNUSED(obj);
     if(code == LV_EVENT_VALUE_CHANGED) {
         LV_LOG_USER("State: %s\n", lv_obj_has_state(obj, LV_STATE_CHECKED) ? "On" : "Off");
     }