Fix hsn_new(1), one-line fix.

[apcraig]

PR checklist

• [X] Short (1 sentence) summary of your PR: Fix hsn_new(1), one-line fix.
• [X] Developer(s): apcraig, eclare, njeffery
• [X] Suggest PR reviewers from list in the column to the right.
• [X] Please copy the PR test results link or provide a summary of testing completed below. Full test suite of Icepack and CICE run on cheyenne, 3 compilers. All results are bit-for-bit.
• How much do the PR code changes differ from the unmodified code?
  • [X] bit for bit
  • [ ] different at roundoff level
  • [ ] more substantial
• Does this PR create or have dependencies on CICE or any other models?
  • [ ] Yes
  • [X] No
• Does this PR add any new test cases?
  • [ ] Yes
  • [X] No
• Is the documentation being updated? ("Documentation" includes information on the wiki or in the .rst files from doc/source/, which are used to create the online technical docs at https://readthedocs.org/projects/cice-consortium-cice/.)
  • [ ] Yes
  • [X] No, does the documentation need to be updated at a later time?
    • [ ] Yes
    • [X] No
• [X] Please provide any additional information or relevant details below:

Closes https://github.com/CICE-Consortium/Icepack/issues/441