power: supply: cpcap-battery: Use accumulator for current and power average

We should not use measured current value for average since we have proper
coulomb counter values available. Using measured current value should
be only used when the value is queried at a higher rate than the 250 ms
rate the coulomb counter is configured to run at.

Cc: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>