Fix check for backword_pos
Author: winglian
Pull request: yes

# What does this PR do?

This fixes what I believe the original intention of this line should have been. @raghavanone ??

original PR here: https://github.com/huggingface/transformers/pull/21237
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Fixes # (issue)


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Comments:
_The documentation is not available anymore as the PR was closed or merged._

cc @pacman100