power: qpnp-bms: do not pull SoC to 0 based on voltage

When the BMS driver was less accurate, a voltage based SOC clamp was
added in order to keep SoC from shutting down the device incorrectly
at higher voltages and from keeping the device on and going into UVLO
at lower voltages.

However, the ADC voltage reads can dip below cutoff momentarily due
to a faulty read or a large current spike. This can cause the SoC
to go to 0 unnaturally.

Fix this by removing the low end of the voltage clamp so SoC does not
get pulled to 0 and shutdown the device with current spikes.

Change-Id: I66ab467956aff755a0949cbf13249aa73a6c7135
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>