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

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

examples/widgets/textarea/lv_example_textarea_1.c

@@ -4,6 +4,7 @@
 static void textarea_event_handler(lv_event_t * e)
 {
     lv_obj_t * ta = lv_event_get_target(e);
+    LV_UNUSED(ta);
     LV_LOG_USER("Enter was pressed. The current text is: %s", lv_textarea_get_text(ta));
 }