Audio: Google RTC audio processing: Mix all channels in mockup

With this change e.g. in all 2ch case all output channels are
mixed with matching microphone and reference channels. It helps
with testing to hear and see that the mockup works.

If any of the buffers is with less channels the output channels
are mixed to minimum channels count of all streams.

The mixed samples are saturated to avoid nasty sounding overflows.

Signed-off-by: Seppo Ingalsuo <seppo.ingalsuo@linux.intel.com>

src/audio/google/google_rtc_audio_processing_mock.c

@@ -10,6 +10,8 @@
 #include <string.h>
 #include <stdint.h>
 
+#include <sof/audio/format.h>
+#include <sof/math/numbers.h>
 #include <rtos/alloc.h>
 #include "ipc/topology.h"
 
@@ -145,11 +147,17 @@ int GoogleRtcAudioProcessingProcessCapture_int16(GoogleRtcAudioProcessingState *
 	int16_t *ref = state->aec_reference;
 	int16_t *mic = (int16_t *) src;
 	int16_t *out = dest;
-	int n;
+	int channels;
+	int n, m;
+
+	channels = MIN(state->num_capture_channels, state->num_aec_reference_channels);
+	channels = MIN(state->num_output_channels, channels);
 
 	memset(dest, 0, sizeof(int16_t) * state->num_output_channels * state->num_frames);
 	for (n = 0; n < state->num_frames; ++n) {
-		*out = *mic + *ref;
+		for (m = 0; m < channels; m++)
+			out[m] = sat_int16((int32_t)mic[m] + ref[m]);
+
 		ref += state->num_aec_reference_channels;
 		out += state->num_output_channels;
 		mic += state->num_capture_channels;