Enable pixel cache on PortInputView

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Views/PortInputView.cs

             Add(m_EdgeControl);
 
             m_Container.visible = m_EdgeControl.visible = m_Control != null;
+            m_Container.clippingOptions = ClippingOptions.ClipAndCacheContents;
         }
 
         protected override void OnStyleResolved(ICustomStyle styles)