[audio] persistent device volume control (#4416)

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-------------------
So, upon investigating AC3 not booting when fw 20+ and overlay applet disabled, i found the leads:
"LibAppletOff" and "AudioTvOutput". By further decoding instructions i've found a guest assert comparing device volume with hdmi volume. Since we implemented no  proper master volume when no streams are created the assert were failing causing guest to panic (why?????????)
Anyway. ac3 now works fw20+ and no overlay applet.. Maybe other games too.

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4416
Reviewed-by: lizzie <lizzie@eden-emu.dev>
Reviewed-by: MaranBr <maranbr@eden-emu.dev>

src/audio_core/sink/cubeb_sink.cpp

@@ -261,6 +261,7 @@ SinkStream* CubebSink::AcquireSinkStream(Core::System& system, u32 system_channe
     system_channels = system_channels_;
     SinkStreamPtr& stream = sink_streams.emplace_back(std::make_unique<CubebSinkStream>(
         ctx, device_channels, system_channels, output_device, input_device, name, type, system));
+    stream->SetDeviceVolume(device_volume);
 
     return stream.get();
 }
@@ -280,14 +281,11 @@ void CubebSink::CloseStreams() {
 }
 
 f32 CubebSink::GetDeviceVolume() const {
-    if (sink_streams.empty()) {
-        return 1.0f;
-    }
-
-    return sink_streams[0]->GetDeviceVolume();
+    return device_volume;
 }
 
 void CubebSink::SetDeviceVolume(f32 volume) {
+    device_volume = volume;
     for (auto& stream : sink_streams) {
         stream->SetDeviceVolume(volume);
     }