Add missing BIND_ENUM for SPEAKER_SURROUND_31

servers/audio_server.cpp

@@ -1297,6 +1297,7 @@ void AudioServer::_bind_methods() {
 	ADD_SIGNAL(MethodInfo("bus_layout_changed"));
 
 	BIND_ENUM_CONSTANT(SPEAKER_MODE_STEREO);
+	BIND_ENUM_CONSTANT(SPEAKER_SURROUND_31);
 	BIND_ENUM_CONSTANT(SPEAKER_SURROUND_51);
 	BIND_ENUM_CONSTANT(SPEAKER_SURROUND_71);
 }