rtc: rv3028: Fix backup-switchover-mode crash

Commit "rtc: rv3028: Mirror BSM and TCE/TCR to EEPROM" was a
forward-port from rpi-5.9.y, and between then and rpi-5.15.y the
rv3028_eeprom_read function was changed from requiring a regmap
pointer to a pointer to the rv3028_data structure. However,
because the declaration specifies a void * pointer, the compiler issues
no warning and the added call to rv3028_eeprom_read leads to an
exception when backup-switchover-mode is used.

See: https://github.com/raspberrypi/linux/issues/2912



Signed-off-by: Phil Elwell <phil@raspberrypi.com>