power: supply: olpc_battery: fix the power supply name

The framework is unhappy about them, because it uses the names in sysfs
attributes:

  power_supply olpc-ac: hwmon: 'olpc-ac' is not a valid name attribute, please fix
  power_supply olpc-battery: hwmon: 'olpc-battery' is not a valid name attribute, please fix

See also commit 648cd48c ("hwmon: Do not accept invalid name
attributes") and commit 74d3b641 ("hwmon: Relax name attribute
validation for new APIs").

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>