power: supply: max17042_battery: mAh readings depend on r_sns value

The PROP_CHARGE_FULL code was hardcoded for the default sense
resistor of 0.010 Ohm, make it use r_sns which contains the
actual sense resistor value in micro-Ohms instead.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>