power: smb5: Disable charger-hw ADC channels before reading USBIN_V

There could be a possible hardware coupling between USBIN_V channel and
other voltage based ADC channel which could lead to false USBIN_OV
interrupts. Fix this by disabling voltage based charger-hw ADC channels
before reading USBIN_V.

Change-Id: I230698c0eeb3a8c646c843a4533f38671484925e
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>
Signed-off-by: Harry Yang <harryy@codeaurora.org>