fix the import path of msda

[jshilong]

Motivation

In open-mmlab/mmcv#978, MultiScaleDeformableAttention has been moved to mmcv/ops/multi_scale_deform_attn.py. We have to fix the import path of MultiScaleDeformableAttention.

BC-breaking

None

[codecov]

Codecov Report

Merging #5338 (8aac58b) into master (238d3f6) will increase coverage by 0.03%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##           master    #5338      +/-   ##
==========================================
+ Coverage   65.07%   65.11%   +0.03%     
==========================================
  Files         275      275              
  Lines       21232    21238       +6     
  Branches     3532     3532              
==========================================
+ Hits        13817    13829      +12     
- Misses       6654     6662       +8     
+ Partials      761      747      -14     

Flag	Coverage Δ
unittests	65.08% <85.71%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
mmdet/models/utils/transformer.py	46.04% <85.71%> (+1.13%)	⬆️
mmdet/models/detectors/cornernet.py	94.87% <0.00%> (-5.13%)	⬇️
mmdet/models/dense_heads/corner_head.py	67.48% <0.00%> (-2.46%)	⬇️
mmdet/models/dense_heads/dense_test_mixins.py	43.58% <0.00%> (+2.56%)	⬆️
mmdet/models/roi_heads/mask_heads/fcn_mask_head.py	73.25% <0.00%> (+3.48%)	⬆️
mmdet/models/roi_heads/test_mixins.py	57.25% <0.00%> (+4.03%)	⬆️
mmdet/models/utils/normed_predictor.py	92.85% <0.00%> (+9.52%)	⬆️

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[noahc1510]

https://github.com/open-mmlab/mmdetection/blob/master/docs/get_started.md
This doc should be update that mmdet==2.13.0 cannot work with mmcv>=1.3.6 because of this change.