Revert "audio: Do not hardcode channel mask to stereo"

This reverts commit 9807bfcf59f4547b825cb7fe0c55599b4754e8f4.

Change-Id: I49066b20e9c42c005555a073f59876ada3ef451c
diff --git a/audio/hal/audio_hw.c b/audio/hal/audio_hw.c
index f853a10..28fdc28 100644
--- a/audio/hal/audio_hw.c
+++ b/audio/hal/audio_hw.c
@@ -2697,6 +2697,7 @@
     in->source = source;
     in->dev = adev;
     in->standby = 1;
+    config->channel_mask = AUDIO_CHANNEL_INDEX_MASK_2;
     in->main_channels = config->channel_mask;
     in->requested_rate = config->sample_rate;
     if (config->sample_rate != CAPTURE_DEFAULT_SAMPLING_RATE)