Clean up baseband processors to each have a main().

firmware/baseband/proc_wfm_audio.cpp

@@ -125,7 +125,8 @@ void WidebandFMAudio::capture_config(const CaptureConfigMessage& message) {
 	}
 }
 
-void run() {
+int main() {
 	EventDispatcher event_dispatcher { std::make_unique<WidebandFMAudio>() };
 	event_dispatcher.run();
+	return 0;
 }