power: reset: st-poweroff: use builtin_platform_driver() to simplify code

The st_reset_init() doesn't do anything special, so it can use the
builtin_platform_driver() macro to eliminate boilerplate code.
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20230807131951.3443880-2-yangyingliang@huawei.comSigned-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/reset/st-poweroff.c

@@ -100,12 +100,7 @@ static struct platform_driver st_reset_driver = {
 	},
 };
 
-static int __init st_reset_init(void)
-{
-	return platform_driver_register(&st_reset_driver);
-}
-
-device_initcall(st_reset_init);
+builtin_platform_driver(st_reset_driver);
 
 MODULE_AUTHOR("Christophe Kerello <christophe.kerello@st.com>");
 MODULE_DESCRIPTION("STMicroelectronics Power off Restart driver");