Fix Typo
# What does this PR do?

Fixed wrong annotation

- `(seq_len, BS, model_dim) -> (BS, seq_len, model_dim)` -> `(BS, seq_len, model_dim) -> (seq_len, BS, model_dim)`

## 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/main/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
Can you check if this is correct @ArthurZucker ?<|||||>_The documentation is not available anymore as the PR was closed or merged._