power: supply: sc27xx: Fix conditon to enable the FGU interrupt

We should allow to enable FGU interrupt to adjust the battery capacity,
when charging status is POWER_SUPPLY_STATUS_DISCHARGING.

Signed-off-by: Yuanjiang Yu <yuanjiang.yu@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>