audio hal: Fix multichannel playback

Correctly operate on input and output buffers in DownmixerBufferProvider

Note that playback is a bit choppy, need to investigate further.

Change-Id: I350175dcc9cc7142a1935585a8bd5e9abb1b8eb6
Test: play back a 5.1 file
diff --git a/media/libaudiohal/EffectBufferHalHidl.cpp b/media/libaudiohal/EffectBufferHalHidl.cpp
index 446d2ef..9a9535b 100644
--- a/media/libaudiohal/EffectBufferHalHidl.cpp
+++ b/media/libaudiohal/EffectBufferHalHidl.cpp
@@ -113,15 +113,25 @@
 }
 
 void EffectBufferHalHidl::update() {
-    if (mExternalData == nullptr) return;
-    mMemory->update();
-    memcpy(mAudioBuffer.raw, mExternalData, mBufferSize);
-    mMemory->commit();
+    update(mBufferSize);
 }
 
 void EffectBufferHalHidl::commit() {
+    commit(mBufferSize);
+}
+
+void EffectBufferHalHidl::update(size_t size) {
     if (mExternalData == nullptr) return;
-    memcpy(mExternalData, mAudioBuffer.raw, mBufferSize);
+    mMemory->update();
+    if (size > mBufferSize) size = mBufferSize;
+    memcpy(mAudioBuffer.raw, mExternalData, size);
+    mMemory->commit();
+}
+
+void EffectBufferHalHidl::commit(size_t size) {
+    if (mExternalData == nullptr) return;
+    if (size > mBufferSize) size = mBufferSize;
+    memcpy(mExternalData, mAudioBuffer.raw, size);
 }
 
 } // namespace android