chore: fix warning when log disable (#5018)

Signed-off-by: FASTSHIFT <vifextech@foxmail.com>

examples/others/observer/lv_example_observer_2.c

@@ -30,6 +30,7 @@ static void engine_state_observer_cb(lv_observer_t * observer, lv_subject_t * su
     LV_UNUSED(observer);
 
     int32_t v = lv_subject_get_int(subject);
+    LV_UNUSED(v);
     /*In a real application set/clear a pin here*/
     LV_LOG_USER("Engine state: %d", v);
 }

examples/widgets/msgbox/lv_example_msgbox_1.c

@@ -5,6 +5,7 @@ static void event_cb(lv_event_t * e)
 {
     lv_obj_t * btn = lv_event_get_target(e);
     lv_obj_t * label = lv_obj_get_child(btn, 0);
+    LV_UNUSED(label);
     LV_LOG_USER("Button %s clicked", lv_label_get_text(label));
 }