Fix decal upgrade script

com.unity.render-pipelines.high-definition/HDRP/Editor/Upgraders/UpgradeMenuItem.cs

 
                 if (maskBlendMode == 0.0f)
                 {
-                    mat.SetFloat("_MaskBlendMode", 4.0f);
+                    mat.SetFloat("_MaskBlendMode", (float)Decal.MaskBlendFlags.Smoothness);
                     return true;
                 }
             }