Fix spelling error in "num_workers" parameter to actually set number of dataset workers specified in yaml configs
Signed-off-by: Michael Menefee <mikem@mnetwork.org>

# What does this PR do ?

Corrects config file parsing to use number of workers specified instead of default "2", which generates warnings and slows training.

**Collection**: NLP

# Changelog 
- Fix spelling error in "num_workers" parameter to actually set number of dataset workers specified in yaml configs

# Usage
* Validating fix - 

```
cd examples/nlp/entity_linking 
vim ./conf/umls_medical_entity_linking_config.yaml
## Change num_workers ~= nproc
python data/umls_dataset_processing.py
python self_alignment_pretraining.py project_dir=. 
## should no longer see num_workers warnings
```

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**PR Type**:
- [ ] New Feature
- [X] Bugfix
- [ ] Documentation

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# Additional Information
* Related to # (issue)
