power: qpnp-bms: fix soc adjustment in high load charging

When the system is under heavy load but still drawing power from the
connected charger and the battery is in constant voltage charging,
the BMS driver never changes back into a constant current charging
state. This can cause random SoC jumps if the system load suddenly
lessens and the BMS driver tries to do constant voltage style SoC
scaling based on battery current.

Fix this by allowing the BMS driver to back out of the constant voltage
charging state.

Change-Id: I61f1d076ca9f623a31aa36960c3fd3ef2b238d78
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>