AudioResampler: Accumulate for multichannel output

Test: Talkback with multichannel USB
Bug: 113697681
Change-Id: I1ca92f6c1abe71cea090bd01b31a4c45cb55e320
diff --git a/media/libaudioprocessing/AudioResamplerFirProcess.h b/media/libaudioprocessing/AudioResamplerFirProcess.h
index a741677..9b70a1c 100644
--- a/media/libaudioprocessing/AudioResamplerFirProcess.h
+++ b/media/libaudioprocessing/AudioResamplerFirProcess.h
@@ -90,7 +90,7 @@
         Accumulator<CHANNELS-1, TO>::acc(coef, data);
     }
     inline void volume(TO*& out, TO gain) {
-        *out++ = volumeAdjust(value, gain);
+        *out++ += volumeAdjust(value, gain);
         Accumulator<CHANNELS-1, TO>::volume(out, gain);
     }