Fix `HfDeepSpeedConfig` argument in `Trainer`
# What does this PR do?

`HfDeepSpeedConfig` accepts a dictionary or a path to `.json` file containing DeepSpeed configurations. However, `self.args` is a `TrainingArgument` object. This PR replaces `self.args` with `self.args.deepspeed`.


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [ ] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [ ] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case.
- [ ] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/master/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/master/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


## Who can review?

@stas00 
_The documentation is not available anymore as the PR was closed or merged._<|||||>With DS please remember the live CI doesn't run any of DS tests as it doesn't have GPUs. So they only run nightly, so it's best to run the tests locally if you have at least one gpu.
```
RUN_SLOW=1 pytest tests/deepspeed
```

I did run the tests and they all pass, so all is good. (Clearly this feature hasn't been tested, but as I said I can't think of how it could be tested in this particular situation).<|||||>Thank you for the comments and review, @stas00. It makes sense that the CI doesn't run DeepSpeed tests every time. 

I can't think of a way to test this right off the bat either, but I'll open an issue and/or a PR if I get any ideas while integrating OSLO!