ARM: dts: msm8926: modify ceiling voltage of nominal mode

New voltage plan requires changing it from 1.16v to 1.15v, so we
change it accordingly.

Change-Id: Idf54897b3f0c0cfa67a524d2ad9c96d72c011c1d
Signed-off-by: Ke Liu <keliu@codeaurora.org>