rtc: ds1307: replace HAS_ALARM by RTC_FEATURE_ALARM

The core now has RTC_FEATURE_ALARM for the driver to indicate whether
alarms are available. Use that instead of HAS_ALARM to ensure the alarm
callbacks are not even called.

Tested-by: Łukasz Stelmach <l.stelmach@samsung.com>
Reviewed-by: Łukasz Stelmach <l.stelmach@samsung.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210418000023.995758-1-alexandre.belloni@bootlin.com