Fix AudioPolicyManagerTestMsd

According to http://ag/28986784, to retrieve output device, the audio
source should remain AUDIO_SOURCE_INVALID.

Change-Id: I6b74767cd25049e4e0f0a5040d904d8de00bd692
Bug: http://b/378534834
Test: AudioPolicyManagerTestMsd
Flag: EXEMPT fix test
1 file changed