max17042_battery: Do not lose accuracy calculating current_now

PROP_CURRENT_NOW value is first divided then multiplied up
causing a lose of accuracy.  Use the same method as
PROP_CURRENT_AVG to do the calculation.

Signed-off-by: Philip Rakity <prakity@marvell.com>
Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>