charger-manager : Replace kzalloc to devm_kzalloc and remove uneccessary code

Use devm function for dynamic memory allocation.

Signed-off-by: Jonghwa Lee <jonghwa3.lee@samsung.com>
Signed-off-by: Myungjoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Anton Vorontsov <anton@enomsg.org>