power: smb5-lib: Fix incorrect ADC channel configuration

ADC channel configuration register is not restored to proper
state as its locally stored value is overwritten. This leads
to a incorrect value being restored which inadvertently effects
the temperature reporting impacting the charge current. Fix this.

Change-Id: I0306b8e6eb38555264a7c2af77dc57d2f5cab463
Signed-off-by: Umang Chheda <uchheda@codeaurora.org>