audio: use 0dB gain for all mixers

A mixer gain of 118 (-2dB) was used to avoid noise caused by
saturation in the ABE. However, this has been fixed with ABE
firmware 9.46, so these gains can be restored to 0dB for
maximum dynamic range.

Change-Id: Id6a6ae5faeac8673faad3444d5e46e6469d5bd2d
1 file changed