Fix val_split

[ethanwharris]

What does this PR do?

Fixes # (issue)

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[codecov]

Codecov Report

Merging #1079 (255d507) into master (f37e50d) will increase coverage by 0.10%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master    #1079      +/-   ##
==========================================
+ Coverage   87.64%   87.75%   +0.10%     
==========================================
  Files         281      281              
  Lines       12793    12793              
==========================================
+ Hits        11212    11226      +14     
+ Misses       1581     1567      -14     

Flag	Coverage Δ
unittests	87.75% <75.00%> (+0.10%)	⬆️

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

Impacted Files	Coverage Δ
flash/core/data/data_module.py	95.23% <75.00%> (+0.34%)	⬆️
flash/text/question_answering/model.py	91.15% <0.00%> (+0.68%)	⬆️
flash/core/integrations/icevision/adapter.py	93.15% <0.00%> (+9.58%)	⬆️
flash/core/data/splits.py	97.14% <0.00%> (+14.28%)	⬆️

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