rtc: max77686: Do not allow interrupt to fire before system resume

The rtc-max77686 device shares the main interrupt line with parent MFD
device (max77686 driver).  During the system suspend, the parent MFD
device disables this IRQ to prevent an early event happening before
resuming I2C bus controller.

The same should be done by rtc-max77686 driver because otherwise the
interrupt handler max77686_rtc_alarm_irq() will be called before its
resume function (max77686_rtc_resume()).  Such issue is not fatal but
disabling shared IRQ by all users ensures correct behavior.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20200615161455.4420-1-krzk@kernel.org