rtc: ds1685: drop no_irq

No platforms are currently setting no_irq. Anyway, letting platform_get_irq
fail is fine as this means that there is no IRQ. In that case, clear
RTC_FEATURE_ALARM so the core knows there are no alarms.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220309162301.61679-2-alexandre.belloni@bootlin.com