lp8727_charger: Unregister power supply at error path of lp8727_register_psy

if usb power supply registration fails,
	we wont unregister the ac power supply
if battery power supply registration fails,
	we wont unregister the usb, and ac supply,

take care of those things and also no need of goto -err_mem: at the fail case of
kzalloc simply can have return -ENOMEM

Signed-off-by: Devendra Naga <develkernel412222@gmail.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>