Enabled the texture streaming debugging update in 2018.2

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Debug/DebugDisplay.cs

 
         public void UpdateMaterials()
         {
-            //if (mipMapDebugSettings.debugMipMapMode != 0)
-            //    Texture.SetStreamingTextureMaterialDebugProperties();
+#if UNITY_2018_2_OR_NEWER
+            if (mipMapDebugSettings.debugMipMapMode != 0)
+                Texture.SetStreamingTextureMaterialDebugProperties();
+#endif
         }
 
         void RegisterDisplayStatsDebug()