rtc: fsl-ftm-alarm: Use module_platform_driver replace device_initcall

The ftm_rtc_driver has been registered while module init, however there
is not unregister step for module exit, now use the macro
module_platform_driver replace device_initcall, which can register and
unregister platform driver automatically.
Signed-off-by: Zhang Jianhua <chris.zjh@huawei.com>
Link: https://lore.kernel.org/r/20220906143037.1455317-1-chris.zjh@huawei.comSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-fsl-ftm-alarm.c

@@ -327,12 +327,7 @@ static struct platform_driver ftm_rtc_driver = {
 	},
 };
 
-static int __init ftm_alarm_init(void)
-{
-	return platform_driver_register(&ftm_rtc_driver);
-}
-
-device_initcall(ftm_alarm_init);
+module_platform_driver(ftm_rtc_driver);
 
 MODULE_DESCRIPTION("NXP/Freescale FlexTimer alarm driver");
 MODULE_AUTHOR("Biwen Li <biwen.li@nxp.com>");