rtc: isl12022: stop using deprecated devm_rtc_device_register()

The comments say that devm_rtc_device_register() is deprecated and
that one should instead use devm_rtc_allocate_device() and
[devm_]rtc_register_device. So do that.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Link: https://lore.kernel.org/r/20220921114624.3250848-2-linux@rasmusvillemoes.dk


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