power: smb1390-psy: Fix taper charge handling

Currently, if taper charging is initiated prior to reduction in float
voltage by external control parameters like JEITA, QNOVO, etc., then
secondary charger termination will happen due to reduction in float
voltage but won't get captured in the SW flow as because the taper-entry
float voltage in only captured during the initiation of taper routine.

Fix this by updating the taper condition float voltage on every iteration
of the taper routine.

Change-Id: Ic437175e150ac18edde30d00afc4146f7516e547
Signed-off-by: Umang Agrawal <uagrawal@codeaurora.org>