power: supply: gpio-charger: Use GPIOF_ACTIVE_LOW for legacy setup

Setting GPIOF_ACTIVE_LOW flag based on platform data gpio_active_low
makes return value of gpiod_get_value_cansleep directly usable.

Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>