BUG: Use Spline order for 3 template parameter.

This commit fixes common mistake of using dimension for spline order. It
was discovered while working on a fix for 0004290 (introduced after integrating
r25482 (ENH: Updating DCMTK to 3.6.1_2016.10.12).

Reviewed-by: Andras Lasso <lasso@queensu.ca>

From: Bradley Lowekamp <blowekamp@mail.nih.gov>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@25485 3bd1e089-480b-0410-8dfb-8563597acbee