Merge "AudioMixer: Fix MONO_EXPAND for more than 2 channels" am: 23c1d67814 am: c7f9c25b39 am: 6afee2b1b9

Original change: https://android-review.googlesource.com/c/platform/frameworks/av/+/1438413

Change-Id: Ie2de5a1709bace27bf175f1d1baafe38d9808f5c