[Bug Fix] Fix fast tokenizer
# What does this PR do ?

Currently the arguments for fast tokenizer are not properly passed through so it cannot be used

**Collection**: [NLP]

# Changelog 
This PR just properly passes the use_fast argument

# Usage

use_fast: True in the config


**PR Type**:
- [ ] Bugfix


## Who can review?

Anyone in the community is free to review the PR once the checks have passed. 
[Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md) contains specific people who can review PRs to various areas.

# Additional Information
* Related to # (issue)
