power: supply: s3c-adc-battery: fix driver data initialization

For power_supply_get_drvdata() routine to work correctly the driver data
has to be provided when registering power supply, otherwise driver gives up
immediately with these errors:

  power_supply main-battery: no battery infos ?!
  power_supply main-battery: driver failed to report `status' property: -22

Signed-off-by: Sergiy Kibrik <sakib@darkstar.site>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>