rtc; pcf2123: fix possible alarm race condition

Clear the flag after disabling the alarm to ensure the alarm doesn't fire
between clearing the flag and disabling the alarm.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20190819182656.29744-2-alexandre.belloni@bootlin.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>