Avoid incompatible audio_port_config

Fix as per b/206668381#comment6

Fixes: 206668381
Test: N/A (see comments)
Change-Id: Idc51d8c6714ac5d10a08b2ddd6471fc8b0546e51
diff --git a/services/audiopolicy/managerdefault/AudioPolicyManager.cpp b/services/audiopolicy/managerdefault/AudioPolicyManager.cpp
index 92140d5..914d0e7 100644
--- a/services/audiopolicy/managerdefault/AudioPolicyManager.cpp
+++ b/services/audiopolicy/managerdefault/AudioPolicyManager.cpp
@@ -4101,7 +4101,7 @@
                     }
                     if (outputDesc != nullptr) {
                         audio_port_config srcMixPortConfig = {};
-                        outputDesc->toAudioPortConfig(&srcMixPortConfig, &patch->sources[0]);
+                        outputDesc->toAudioPortConfig(&srcMixPortConfig, nullptr);
                         // for volume control, we may need a valid stream
                         srcMixPortConfig.ext.mix.usecase.stream = sourceDesc != nullptr ?
                                     sourceDesc->stream() : AUDIO_STREAM_PATCH;