power: supply: core: Update sysfs-class-power ABI document

Add the "Over Current" string to /sys/class/power_supply/<supply_name>/health
description.

Fixes: e3e83cc6

 ("power: supply: core: Add POWER_SUPPLY_HEALTH_OVERCURRENT constant")
Signed-off-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>