We should terminate charging when we reach the voltage_max_design_uv
not overvoltage_limit_uv, this is an abuse of that struct member.

The overvoltage limit is actually not configurable on the AB8500,
it is fixed to 4.75 V so drop a comment about that in the code.

Fixes: 2a5f4183 ("power: supply: ab8500: Standardize voltages")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>