rtc: pm8xxx: fix set-alarm race

rtc: pm8xxx: fix set-alarm race

Make sure to disable the alarm before updating the four alarm time
registers to avoid spurious alarms during the update.

Note that the disable needs to be done outside of the ctrl_reg_lock
section to prevent a racing alarm interrupt from disabling the newly set
alarm when the lock is released.

Fixes: 9a9a54ad7aa2 ("drivers/rtc: add support for Qualcomm PMIC8xxx RTC")
Cc: stable@vger.kernel.org      # 3.1
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Reviewed-by: David Collins <quic_collinsd@quicinc.com>
Link: https://lore.kernel.org/r/20230202155448.6715-2-johan+linaro@kernel.org
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>