ARM: dts: msm: Request headset micbias2 with 1.8v

Request micbias to 1.8v instead of 2.7v for 8996 target.
This is sufficient to detect most of the headset
accessories.

Change-Id: If1e0b596905c8dc5b3cab9c33339d1f2b206a80c
Signed-off-by: Phani Kumar Uppalapati <phaniu@codeaurora.org>