Added sound volume slider to HLE sound plugin, currently DSound only, unless someone wants to add it to OpenAL :p

git-svn-id: https://dolphin-emu.googlecode.com/svn/trunk@3262 8ced0084-cf51-0410-be5f-012b33b47a6e

Source/Core/AudioCommon/Src/SoundStream.h

@@ -40,6 +40,7 @@ public:
 	static  bool isValid() { return false; }  
 	virtual CMixer *GetMixer() const { return m_mixer; }
 	virtual bool Start() { return false; }
+	virtual void SetVolume(int) {}
 	virtual void SoundLoop() {}
 	virtual void Stop() {}
 	virtual void Update() {}