power: qpnp-charger: enable IR drop compensation

Change from using VPH_PWR sense to VBAT_SNS to
regulate VBAT. This should allow the charger
to correctly regulate vbat at 4.2V when
end of charge is approaching.

Change-Id: Ic1daa6197f5309a8b5b326a321f2b8a30e58bf27
Signed-off-by: David Keitel <dkeitel@codeaurora.org>