power: supply: axp288_charger: Use devm_power_supply_register

Use devm_power_supply_register instead of power_supply_register,
this avoids the need to do manual cleanup and results in quite
a nice code cleanup.

Note it may seem excessive to add a "struct device *dev" helper local
variable for the 1 time it is used in this patch, but future patches
in this series also use it.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>