Fix VTK compatibility

https://github.com/fran6co/pcl/commit/4d1ee479e8fc791b5a7b0f75ecb109105bbe6d48#diff-4206b5bbfa76680243fec88c91dfbd3cL119 removed the update call which is in fact needed for VTK 5. It does not hurt VTK6 support.