将button_handler函数设为内部函数

from: https://github.com/0x1abin/MultiButton/pull/38/commits/41514fed4b99263f0e41efce658934d6c4a27062

multi_button.c

@@ -65,7 +65,7 @@ PressEvent get_button_event(struct button* handle)
   * @param  handle: the button handle strcut.
   * @retval None
   */
-void button_handler(struct button* handle)
+static void button_handler(struct button* handle)
 {
     uint8_t read_gpio_level = handle->hal_button_Level();