power: smb1398: set DIV2_CP switch phase-shift while reading isns

Incorrect lower ISNS is seen when both master and slave CPs are enabled.
Fix this by using a 0 degree phase-shift between master/slave while
reading the ISNS.

Change-Id: I4a2199d5fb487bec087eda412103c9c45aa0a96c
Signed-off-by: Ashish Chavan <ashichav@codeaurora.org>