extcon: max8997: Use devm_extcon_dev_register()

extcon: max8997: Use devm_extcon_dev_register()

Use the resource-managed extcon device register function (i.e.
devm_extcon_dev_register()) instead of extcon_dev_register(). If extcon device
is attached with this function, that extcon device is automatically unregistered
on driver detach. That reduces tiresome managing code.

Signed-off-by: Sangjung Woo <sangjung.woo@samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>