power: supply: charger-manager: Swap private uevent for power_supply_changed

Whenever the battery status is changed, charger manager triggers a uevent
through a private interface. Modify it to use power_supply_changed()
since it belongs to the power supply subsystem.

Signed-off-by: Jonghwa Lee <jonghwa3.lee@samsung.com>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Jonathan Bakker <xc-racer2@live.ca>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>