power: supply: ab8500_fg: Safeguard compensated voltage

In some cases when the platform is dissapating more than
500mA the voltage measurements and compensation will become
instable. Add a parameter to bail out of the voltage
measurement if this happens.

This code was found in a Samsung vendor tree.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>