rtc: pcf2127: adapt for CLKOUT register at any offset

This will simplify the implementation of new variants into this driver.

Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Reviewed-by: Bruno Thomsen <bruno.thomsen@gmail.com>
Link: https://lore.kernel.org/r/20230622145800.2442116-10-hugo@hugovil.com


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