ARM: dts: msm: correct BT_EN pin drive voltage for SDXPRAIRIE

bluetooth enable pin belongs to 1.8V power domain based on relevant
spec, but the pin is driven with 3.3V when enable bluetooth and
results in current leakage issue, so correct drive voltage to 1.8V.

CRs-Fixed: 2518416
Change-Id: I7d0d475717e80de71136d8f58df2d526e646912a
Signed-off-by: Zijun Hu <zijuhu@codeaurora.org>