Fix depth stencil errors.
Fix depth stencil errors.

- D3D12 ERROR: ID3D12CommandList::DrawIndexedInstanced: The depth stencil format does not match that specified by the current pipeline state. A null view must be bound when the pipeline state format is UNKNOWN. (pipeline state = UNKNOWN, depth stencil view = D24_UNORM_S8_UINT, ID3D12Resource* = 0x0A1BEC60:'Unnamed ID3D12Resource Object') [ EXECUTION ERROR #615: DEPTH_STENCIL_FORMAT_MISMATCH_PIPELINE_STATE]
- D3D12 WARNING: ID3D12CommandList::ClearDepthStencilView: The application did not pass any clear value to resource creation. The clear operation is typically slower as a result; but will still clear to the desired value. [ EXECUTION WARNING #821: CLEARDEPTHSTENCILVIEW_MISMATCHINGCLEARVALUE]

yorung/dx12playground,yorung/dx12playground