Fix unit conversion

[atztogo]

Unit conversion was property performed for non-VASP calculators. This PR attempts to fix it.

[codecov]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (a12cfe0) 62.09% compared to head (3d50a56) 61.91%.

❗ Current head 3d50a56 differs from pull request most recent head ed39f74. Consider uploading reports for the commit ed39f74 to get more accurate results

Files	Patch %	Lines
phono3py/cui/create_force_constants.py	55.00%	9 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #191      +/-   ##
===========================================
- Coverage    62.09%   61.91%   -0.19%     
===========================================
  Files           70       70              
  Lines        12482    12493      +11     
===========================================
- Hits          7751     7735      -16     
- Misses        4731     4758      +27     

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