power: supply: axp288_fuel_gauge: Read 12 bit values 2 registers at a time

[ Upstream commit 248efcf00602f0282587999bcc221a872bd72530 ]

In order for the MSB -> LSB latching to work correctly we must read the
2 8 bit registers of a 12 bit value in one consecutive read.

This fixes voltage_ocv reporting inconsistent values on my tablet.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>