gpio: mb86s7x: use builtin_platform_driver

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

drivers/gpio/gpio-mb86s7x.c

@@ -217,8 +217,4 @@ static struct platform_driver mb86s70_gpio_driver = {
 	.remove = mb86s70_gpio_remove,
 };
 
-static int __init mb86s70_gpio_init(void)
-{
-	return platform_driver_register(&mb86s70_gpio_driver);
-}
-device_initcall(mb86s70_gpio_init);
+builtin_platform_driver(mb86s70_gpio_driver);