max8997_charger: Needs module.h

power/max8997_charger.c uses interfaces from linux/module.h,
so it should include that file.  This fixes build errors.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>