max17042_battery: Fix CHARGE_FULL representation.

CHARGE_FULL should represent the full capacity of the battery in uAh.
The 0x10 (FullCAP) register shows the compensated full capacity in
mAh * 2; e.g., reg(0x10) = 0xBB8 means that it is 1500mAh.

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>