D3DBase: Create the swapchain in fullscreen mode if enabled.

Source/Core/VideoBackends/D3D12/D3DBase.h

@@ -124,7 +124,7 @@ const std::string VertexShaderVersionString();
 unsigned int GetMaxTextureSize();
 
 HRESULT SetFullscreenState(bool enable_fullscreen);
-HRESULT GetFullscreenState(bool* fullscreen_state);
+bool GetFullscreenState();
 
 // This function will assign a name to the given resource.
 // The DirectX debug layer will make it easier to identify resources that way,