Fix loss function buffer support

[ethanwharris]

What does this PR do?

Fixes # (issue)

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[codecov]

Codecov Report

Merging #1203 (3bf6ad0) into master (3c06c3f) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1203      +/-   ##
==========================================
+ Coverage   90.95%   90.96%   +0.01%     
==========================================
  Files         284      284              
  Lines       12686    12689       +3     
==========================================
+ Hits        11539    11543       +4     
+ Misses       1147     1146       -1     

Flag	Coverage Δ
unittests	90.96% <100.00%> (+0.01%)	⬆️

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

Impacted Files	Coverage Δ
flash/core/utilities/apply_func.py	94.11% <100.00%> (+1.26%)	⬆️
flash/text/question_answering/model.py	92.56% <0.00%> (+0.67%)	⬆️

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[krshrimali]

Nice 🎉 LGTM, thanks @ethanwharris