[Fix] Fix RAFT wrong refine iter after evaluation

[MeowZheng]

Motivation

As refine iterations when model testing is different from model training, it used test_cfg to modify iter of the model when testing but forgot to recover the iter for training.

[codecov]

Codecov Report

Merging #62 (0db516d) into master (2f98716) will increase coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #62      +/-   ##
==========================================
+ Coverage   66.97%   67.07%   +0.10%     
==========================================
  Files          83       83              
  Lines        4723     4726       +3     
  Branches      678      678              
==========================================
+ Hits         3163     3170       +7     
+ Misses       1457     1453       -4     
  Partials      103      103              

Flag	Coverage Δ
unittests	67.07% <100.00%> (+0.10%)	⬆️

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Impacted Files	Coverage Δ
mmflow/models/flow_estimators/raft.py	83.33% <100.00%> (+0.98%)	⬆️
mmflow/datasets/pipelines/transforms.py	78.66% <0.00%> (+0.66%)	⬆️

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