rtc: isl12022: Replace uint8_t types with u8

Keep coding style consistent, by using kernel integer types instead of
standard types.

Signed-off-by: Esben Haabendal <esben@geanix.com>
Link: https://lore.kernel.org/r/20240913-rtc-isl12022-alarm-irq-v2-3-37309d939723@geanix.com


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