BUG: fix typo and warning in diffusion tensor scalars

One of the command line argument parsing options was misspelled.

Also there was an extra SetInput that caused a warning message.

Thanks to Vadim vadmalis@gmail.com for pointing this out.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21915 3bd1e089-480b-0410-8dfb-8563597acbee