power: pm8921-bms: compensate ocv for ir drops

The ocv could be taken when there is some current being pushed or
drawn from the battery. Compensate for the drop across battery
resistance and connector resistance for ocv.

Change-Id: I9eaf7f21c73dd1ceaf97589cbf82b722706c48c2
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>