Fix a copy-paste error

Assets/ScriptableRenderPipeline/HDRenderPipeline/HDRenderPipeline.cs

             m_FilterSubsurfaceScattering.SetFloat("_DstBlend", (float)BlendMode.Zero);
 
             m_FilterAndCombineSubsurfaceScattering = Utilities.CreateEngineMaterial("Hidden/HDRenderPipeline/CombineSubsurfaceScattering");
-            m_FilterSubsurfaceScattering.EnableKeyword("FILTER_HORIZONTAL_AND_COMBINE");
+            m_FilterAndCombineSubsurfaceScattering.EnableKeyword("FILTER_HORIZONTAL_AND_COMBINE");
             m_FilterAndCombineSubsurfaceScattering.SetFloat("_DstBlend", (float)BlendMode.One);
 
             InitializeDebugMaterials();