dzn, d3d12: Fix path passed to CreateDeviceFactory
Appending d3d12core.dll to the path is great for checking if the file exists, but then we need to remove it again because CreateDeviceFactory expects a directory path, not a file path.
Appending d3d12core.dll to the path is great for checking if the file exists, but then we need to remove it again because CreateDeviceFactory expects a directory path, not a file path.