rtc: pcf8563: fix wrong alarm register

rtc: pcf8563: fix wrong alarm register

When the regmap framework was introduced to this driver,
the PCF8563_REG_AMN register within the set_alarm function was
incorrectly changed to PCF8563_REG_SC.

The PCF8563_REG_SC register is the seconds register.
This caused alarm values to be written to the seconds register
when an alarm was set. Which means the alarm would not trigger
as expected and the seconds register would be overwritten
with an incorrect value.

Signed-off-by: Troy Mitchell <troymitchell988@gmail.com>
Link: https://lore.kernel.org/r/20250531-pcf8563-fix-alarm-v2-1-cac4b1716167@gmail.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>