HDRenderPipeline: Reassign default material

Assets/ScriptableRenderPipeline/HDRenderPipeline/HDRenderPipelineAsset.asset

     m_ShadowCascadeSplit2: 0.3
     m_ShadowNearPlaneOffset: 5
   m_SkySettings: {fileID: 0}
-  m_DefaultDiffuseMaterial: {fileID: 0}
-  m_DefaultShader: {fileID: 0}
+  m_DefaultDiffuseMaterial: {fileID: 2100000, guid: 73c176f402d2c2f4d929aa5da7585d17,
+    type: 2}
+  m_DefaultShader: {fileID: 4800000, guid: 6e4ae4064600d784cac1e41a9e6f2e59, type: 3}