Enabled last split fade.

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Shadows/HDShadowSettings.cs

                 m_CascadeShadowBorders[2] = cascadeShadowBorder2;
                 m_CascadeShadowBorders[3] = cascadeShadowBorder3;
 
-
-                /* Borders are currently broken if cascade count is not 4. Enable this when it's fixed.
-                }
-                */
+                }                
                 return m_CascadeShadowBorders;
             }
         }