pinctrl: mediatek: use builtin_platform_driver

Use builtin_platform_driver() helper to simplify the code.
Signed-off-by: Geliang Tang <geliangtang@gmail.com>
Acked-by: Hongzhou Yang <hongzhou.yang@mediatek.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/mediatek/pinctrl-mt6397.c

@@ -64,8 +64,4 @@ static struct platform_driver mtk_pinctrl_driver = {
 	},
 };
 
-static int __init mtk_pinctrl_init(void)
-{
-	return platform_driver_register(&mtk_pinctrl_driver);
-}
-device_initcall(mtk_pinctrl_init);
+builtin_platform_driver(mtk_pinctrl_driver);