power: qpnp-bms: Always setup vbat monitoring

Previously, the BMS driver skips adc-tm vbat monitor setup if it
detects that there is no battery. This is incorrect since a battery
could be inserted later. Not setting up the monitor parameters can
lead to issues later when the battery is actually inserted.

Fix this by always setting up the adc-tm vbat monitor parameters
and simply disabling the channel if there is no battery inserted.

Change-Id: I6980d2b67641fe48644970179fa5a04ddbdc479e
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>