power: supply: axp288_fuel_gauge: Store struct device pointer in axp288_fg_info

Directly store the struct device pointer in axp288_fg_info, rather then
storing a pointer to the struct platform_device there and then using
"&info->pdev->dev" everywhere.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>