power: supply: rt5033_battery: Change voltage values to µV

Currently the rt5033_battery driver provides voltage values in mV. It
should be µV as stated in Documentation/power/power_supply_class.rst.

Fixes: b847dd96 ("power: rt5033_battery: Add RT5033 Fuel gauge device driver")
Cc: Beomho Seo <beomho.seo@samsung.com>
Cc: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Jakob Hauser <jahau@rocketmail.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>