NO_IRQ may be defined as '(unsigned int) -1' in some architectures (arm,
sh ...), and either may not be defined in some architectures (arm64) which
can enable RTC_DRV_S3C.
Also since platform_get_irq returns err-code in case of any error, we do
not need to intialize s3c_rtc_alarmno and s3c_rtc_tickno.