Fix normalizing video classification input

[dudeperf3ct]

What does this PR do?

Fixes #1193

Additional comment: Added a new lambda temporary function to avoid pickling error while training on multiple gpus as proposed in facebookresearch/pytorchvideo#101

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[codecov]

Codecov Report

Merging #1213 (e8fa233) into master (c38b6d9) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1213   +/-   ##
=======================================
  Coverage   90.96%   90.96%           
=======================================
  Files         284      284           
  Lines       12694    12696    +2     
=======================================
+ Hits        11547    11549    +2     
  Misses       1147     1147           

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/video/classification/input_transform.py	100.00% <100.00%> (ø)

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[ethanwharris]

Awesome!!! LGTM 😃 Just a small suggestion. @dudeperf3ct Could you also add a Fixed entry to the CHANGELOG?

[ethanwharris]

Nice! LGTM 😃