Fix for issue 1145: add enableRandomWrite for the color pyramid surfaces

ScriptableRenderPipeline/HDRenderPipeline/HDRP/RenderPipelineResources/BufferPyramid.cs

 
         public void CreateBuffers()
         {
-            m_ColorPyramidBuffer = RTHandle.Alloc(size => CalculatePyramidSize(size), filterMode: FilterMode.Trilinear, colorFormat: RenderTextureFormat.ARGBHalf, sRGB: false, useMipMap: true, autoGenerateMips: false, name: "ColorPymarid");
+            m_ColorPyramidBuffer = RTHandle.Alloc(size => CalculatePyramidSize(size), filterMode: FilterMode.Trilinear, colorFormat: RenderTextureFormat.ARGBHalf, sRGB: false, useMipMap: true, autoGenerateMips: false, enableRandomWrite: true, name: "ColorPyramid");
             m_DepthPyramidBuffer = RTHandle.Alloc(size => CalculatePyramidSize(size), filterMode: FilterMode.Trilinear, colorFormat: RenderTextureFormat.RGFloat, sRGB: false, useMipMap: true, autoGenerateMips: false, enableRandomWrite: true, name: "DepthPyramid"); // Need randomReadWrite because we downsample the first mip with a compute shader.
         }