ARM: dts: msm: adjust S4C voltage

Adjust S4C output voltage to 1.37v for QCA6690 to keep align with
BT settings.

Otherwise bt vote for S4C will fail due to voltage level mismatch
with previous wlan vote.

Change-Id: I7026445ee84ecca09db1d8840b7f63ede9f89fa7
Signed-off-by: Xiaoning Ma <mxiaonin@codeaurora.org>