DSPEmulator: Make the IsLLE() member function const-qualified

This function only queries state and doesn't modify it, so this can be
made a const member function

Source/Core/Core/DSPEmulator.h

@@ -13,7 +13,7 @@ class DSPEmulator
 {
 public:
   virtual ~DSPEmulator();
-  virtual bool IsLLE() = 0;
+  virtual bool IsLLE() const = 0;
 
   virtual bool Initialize(bool wii, bool dsp_thread) = 0;
   virtual void Shutdown() = 0;