[AMP][Bugfix] Fix AMP + SQuAD

[sxjscience]

Description

Tiny fix of the amp for log_maskedsoftmax

Checklist

Essentials

• [x] PR's title starts with a category (e.g. [BUGFIX], [MODEL], [TUTORIAL], [FEATURE], [DOC], etc)
• [x] Changes are complete (i.e. I finished coding on this PR)
• [ ] All changes have test coverage
• [x] Code is well-documented

cc @dmlc/gluon-nlp-team

[github-actions[bot]]

The documentation website for preview: http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR1433/fix_amp/index.html

[github-actions[bot]]

The documentation website for preview: http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR1433/fix_amp/index.html

[codecov[bot]]

Codecov Report

Merging #1433 (1f581e0) into master (84391ef) will decrease coverage by 0.25%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #1433      +/-   ##
==========================================
- Coverage   85.55%   85.30%   -0.26%     
==========================================
  Files          53       53              
  Lines        6987     6987              
==========================================
- Hits         5978     5960      -18     
- Misses       1009     1027      +18     

Impacted Files	Coverage Δ
src/gluonnlp/attention_cell.py	73.72% <0.00%> (-6.67%)	:arrow_down:
src/gluonnlp/utils/parameter.py	92.30% <0.00%> (-1.93%)	:arrow_down:
src/gluonnlp/data/tokenizers/subword_nmt.py	78.50% <0.00%> (-0.94%)	:arrow_down:
src/gluonnlp/data/tokenizers/yttm.py	82.75% <0.00%> (+0.86%)	:arrow_up:

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[github-actions[bot]]

The documentation website for preview: http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR1433/fix_amp/index.html