[Fix] fix add_mim_extension typo in setup.py

[ZCMax]

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Motivation

fix add_mim_extension typo in setup.py

Modification

fix add_mim_extension typo in setup.py

BC-breaking (Optional)

Does the modification introduce changes that break the back-compatibility of the downstream repos?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[codecov]

Codecov Report

Merging #1574 (693a212) into dev (42ee0e7) will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##              dev    #1574      +/-   ##
==========================================
- Coverage   50.19%   50.16%   -0.04%     
==========================================
  Files         223      223              
  Lines       19104    19104              
  Branches     3134     3134              
==========================================
- Hits         9590     9584       -6     
- Misses       8935     8941       +6     
  Partials      579      579              

Flag	Coverage Δ
unittests	50.16% <ø> (-0.04%)	⬇️

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Impacted Files	Coverage Δ
mmdet3d/datasets/pipelines/transforms_3d.py	87.39% <0.00%> (-0.86%)	⬇️

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