power: vm-bms: update PON OCV measurement

In PM8916 2.0 PON OCV calculation is delayed due to change
in the ordering of power-on sequence of LDOs. Adjust PON
OCV measurement to include current during power-on.

CRs-Fixed: 682645
Change-Id: Ia8535a14c79bbe8421305831b766d73383277951
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>