power: supply: axp288_fuel_gauge: Add axp288_fuel_gauge_read_initial_regs()

Refactor probe a bit, introducing a new
axp288_fuel_gauge_read_initial_regs() helper. This replaces a whole
bunch of gotos and removes the unblock_punit_i2c_access label.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>