Init gain config to prevent uninit leak.

In AudioPortConfig, we only initialize index for audio_gain_config, but
not other fields. That may cause uninit leak at listAudioPorts and
listAudioPatches.

Bug: 77238250
Bug: 77238762
Test: try repo steps at the bug description.
Change-Id: I57e3bd0598f9aa698a6fa3d3c0218b046de34e2f
(cherry picked from commit ebe0777edcf3b9c6bde9771d65399e2363dc6e40)
diff --git a/services/audiopolicy/common/managerdefinitions/src/AudioPort.cpp b/services/audiopolicy/common/managerdefinitions/src/AudioPort.cpp
index fcf9070..cdaffe7 100644
--- a/services/audiopolicy/common/managerdefinitions/src/AudioPort.cpp
+++ b/services/audiopolicy/common/managerdefinitions/src/AudioPort.cpp
@@ -385,6 +385,7 @@
     mSamplingRate = 0;
     mChannelMask = AUDIO_CHANNEL_NONE;
     mFormat = AUDIO_FORMAT_INVALID;
+    memset(&mGain, 0, sizeof(struct audio_gain_config));
     mGain.index = -1;
 }