COMP: add GetPointer to vtkNew'd matrices
On ubuntu 16.04 (gcc 5.4) the vtkMatrix4x4 is not coerced to a pointer automatically. Adding GetPointer is consistent with other usages in this file and solves the compile issue.
On ubuntu 16.04 (gcc 5.4) the vtkMatrix4x4 is not coerced to a pointer automatically. Adding GetPointer is consistent with other usages in this file and solves the compile issue.