Use managed resource function devm_power_supply_register instead of
power_supply_register to simplify the error path by allowing unregistering
to happen automatically on error and remove.
Removing max8997_battery_remove function also as it is now redundant.

Also removing out of memory printk message after kzalloc as there is
already enough information on failure.
Signed-off-by: Srikant Ritolia <s.ritolia@samsung.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>