power: qpnp-fg: allow reconfiguration of thermistor control setting

Currently, we configure the FG SRAM register 0x4AF only if the
qcom,sw-rbias-control property is specified through device tree.
However, if that property is not specified for a device anymore
where it was specified before, previous configuration would be
retained unless there is a dVdd reset. Reconfigure the register
0x4AF to allow the default thermistor settings in such cases.

CRs-Fixed: 880044
Change-Id: Ic9bbea3d68968c39bf9b66532278178de9104b24
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>