DVDInterface: Remove GetVolume

For thread safety reasons, the currently inserted volume must
only be accessed by the DVD thread (or by the CPU thread if it
calls DVDThread::WaitUntilIdle() first). After this commit,
only DVDThread.cpp can access the volume, which prevents code in
other files from accessing the volume in a non-threadsafe way.

Source/Core/Core/IOS/DI/DI.cpp

@@ -12,6 +12,7 @@
 #include "Common/Logging/Log.h"
 #include "Common/MsgHandler.h"
 #include "Core/HW/DVD/DVDInterface.h"
+#include "Core/HW/DVD/DVDThread.h"
 #include "Core/HW/Memmap.h"
 #include "Core/IOS/DI/DI.h"
 #include "Core/IOS/ES/ES.h"
@@ -106,10 +107,10 @@ IPCCommandResult DI::IOCtlV(const IOCtlVRequest& request)
     INFO_LOG(IOS_DI, "DVDLowOpenPartition: partition_offset 0x%016" PRIx64, partition_offset);
 
     // Read TMD to the buffer
-    const IOS::ES::TMDReader tmd = DVDInterface::GetVolume().GetTMD();
+    const IOS::ES::TMDReader tmd = DVDThread::GetTMD();
     const std::vector<u8> raw_tmd = tmd.GetRawTMD();
     Memory::CopyToEmu(request.io_vectors[0].address, raw_tmd.data(), raw_tmd.size());
-    ES::DIVerify(tmd, DVDInterface::GetVolume().GetTicket());
+    ES::DIVerify(tmd, DVDThread::GetTicket());
 
     return_value = 1;
     break;