[Fix] Always map location to cpu when loading checkpoint

[gaotongxiao]

Motivation

See open-mmlab/mmdetection#6405

[codecov]

Codecov Report

Merging #567 (2159aae) into main (80741e1) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

❗ Current head 2159aae differs from pull request most recent head 4e2cf3d. Consider uploading reports for the commit 4e2cf3d to get more accurate results

@@            Coverage Diff             @@
##             main     #567      +/-   ##
==========================================
- Coverage   85.67%   85.66%   -0.02%     
==========================================
  Files         142      142              
  Lines        9543     9542       -1     
  Branches     1364     1364              
==========================================
- Hits         8176     8174       -2     
+ Misses       1052     1051       -1     
- Partials      315      317       +2     

Flag	Coverage Δ
unittests	85.66% <0.00%> (-0.02%)	⬇️

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Impacted Files	Coverage Δ
mmocr/apis/inference.py	69.56% <0.00%> (+0.59%)	⬆️
mmocr/datasets/pipelines/transforms.py	83.99% <0.00%> (-0.34%)	⬇️

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