power: supply: sbs-battery: Correct supply status with current draw

The status reported directly by the battery controller is not always
reliable and should be corrected based on the current draw information.

This implements such a correction with a dedicated function, called
where the supply status is retrieved.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>