power: supply: max17042_battery: Check battery current for status when supplied

Even though the system is supplied, it may still be discharging if the
supply is e.g. only delivering 5V 0.5A. Check the avg battery current if
available for more accurate status reporting.

Cc: James <kernel@madingley.org>
Suggested-by: James <kernel@madingley.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>