fix typos in error messages in speech recognition example and modelcard.py
# What does this PR do?
This PR fixes two minor typographical issues
1 - a typo in an example speech recognition script that misstates which columns is missing from the input data
2 - a typo in the modelcard.py function that explains when some field is missing from a dataset


## Before submitting
- [X] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [X] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?

## Who can review?
@patrickvonplaten per git blame, but realistically anyone
@sgugger