rtc: rv3028: ensure ram configuration registers are saved

If RV3028_CTRL1_EERD is not set (this is the default), the RTC will refresh
the RAM configuration registers from the EEPROM at midnight. It is
necessary to save the RAM registers back to EEPROM after modifying them.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20201009153101.721149-4-alexandre.belloni@bootlin.com