rtc: pm8xxx: clean up comments

Clean up the driver comments somewhat and remove obsolete, incorrect or
redundant ones.

Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Reviewed-by: David Collins <quic_collinsd@quicinc.com>
Link: https://lore.kernel.org/r/20230202155448.6715-12-johan+linaro@kernel.org


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