Fix an error for a 'DistributedDataParallel' object

[jianguoz]

Fix error to address the AttributeError: 'DistributedDataParallel' object has no attribute 'tokenize_query' in distributed evaluation

Patch description

Fix error in the RAG model to address the AttributeError: 'DistributedDataParallel' object has no attribute 'tokenize_query in distributed evaluation.

Testing steps

(referring to an internal task)

parlai mp_eval  \
-t wizard_of_wikipedia \
--datatype test  \
--skip-generation False \
--batchsize 8 \
--model-file zoo:hallucination/bart_fid_rag/model \
--metrics all \
--n-docs 1 \
--model-parallel false \
--log-every-n-secs 30 

Other information

[klshuster]

thanks for the catch!