ARM: dts: msm: Add CWB mixer preference for sm8150

Update mixer preferences for sm8150 to ensure mixer
allocation is successful and concurrent writeback
feature works fine.

Change-Id: Ic37ee397c3c1c2826683898bc531e303c7c1e5aa
Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>