After modularization, vtkIVWriter was removed because of a dependency
on AbstractMapper. This patch replaces the static call to
vtkAbstractMapper::GetScalars(pd, VTK_SCALAR_MODE_USE_POINT_DATA, 0,
  0, NULL, offset);
with an equivalent call:vtkDataArray *scalars =
pd->GetPointData()->GetScalars();

Change-Id: Ic0f5b5f8f470776e61d8f6684bf0acc386507f71