power: supply: Fix indentation and some other warnings

These were mentioned by checkpatch:
	Errors:
		(1) code indent should use tabs where possible
		(2) switch and case should be at the same indent
	Warnings:
		(1) Missing a blank line after declarations

Signed-off-by: Charalampos Mitrodimas <charmitro@posteo.net>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>