DVDInterface: Translate Wii partition offsets for timing purposes

Until now, Dolphin has been using the wrong values
for calculating DVD timing for decrypted Wii reads
(which Wii games essentially always use).

Source/Core/DiscIO/Volume.h

@@ -37,6 +37,7 @@ public:
 
   virtual bool GetTitleID(u64*) const { return false; }
   virtual std::vector<u8> GetTMD() const { return {}; }
+  virtual u64 PartitionOffsetToRawOffset(u64 offset) const { return offset; }
   virtual std::string GetGameID() const = 0;
   virtual std::string GetMakerID() const = 0;
   virtual u16 GetRevision() const = 0;