Fix HRSC filename

[liuyanyi]

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Motivation

Add img_prefix for HRSC Datset.

Modification

Please briefly describe what modification is made in this PR.

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. The documentation has been modified accordingly, like docstring or example tutorials.

[yangxue0827]

LGTM

[codecov]

Codecov Report

Merging #329 (cac182c) into dev (3055b56) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##              dev     #329      +/-   ##
==========================================
- Coverage   31.59%   31.57%   -0.03%     
==========================================
  Files         113      113              
  Lines        7355     7354       -1     
  Branches     1128     1128              
==========================================
- Hits         2324     2322       -2     
+ Misses       4929     4928       -1     
- Partials      102      104       +2     

Flag	Coverage Δ
unittests	31.57% <0.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmrotate/datasets/hrsc.py	18.03% <0.00%> (ø)
mmrotate/utils/setup_env.py	88.00% <0.00%> (-4.00%)	⬇️
mmrotate/datasets/builder.py	48.14% <0.00%> (-3.71%)	⬇️
mmrotate/apis/inference.py	0.00% <0.00%> (ø)

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