power: qpnp-bms: recalculate SoC faster when vbat is low

Sometimes the BMS accumulates errors through faulty OCVs or small
coulomb counters inaccuracies. These errors can add up when doing high
load discharging, and can make the device go into UVLO without having
the BMS driver report 0% SoC.

Allow the BMS to correct faster if the battery voltage is almost at
cutoff.

Change-Id: Ic19b992d0da954a18cf5357db31dc5c0ffa09812
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>