power: vm-bms: Clamp SOC at v-cutoff during discharge

Due to immaturities of the VBMS hw/sw there is a possibility
of SOC inaccuracy near the cutoff-voltage. In such cases
to avoid pre-mature reporting of SOC = 0, clamp the SOC to
1 if the VBMS calculated SOC is 0 and the battery voltage is
above the cutoff-voltage.

Change-Id: I11bdfec5a67ceead91412a20ea57dad2808228d8
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>