ARM: dts: msm: Fix the prescaling ratio of vchg_sns

Fix the prescaling ratio of vchg_sns VADC channel
to support divide by eight for correct VADC readings.

CRs-Fixed: 598826
Change-Id: I9f9648a8ef451d982a325e4a3845cc10a3269dad
Signed-off-by: Dipen Parmar <dipenp@codeaurora.org>