Problem loading voxpopuli dataset 
### Describe the bug

```
Exception has occurred: FileNotFoundError
Couldn't find file at https://huggingface.co/datasets/facebook/voxpopuli/resolve/main/{'en': 'data/en/asr_train.tsv'}
```

Error in logic for link url creation. The link should be  https://huggingface.co/datasets/facebook/voxpopuli/resolve/main/data/en/asr_train.tsv 

Basically there should be links directly under ```metadata["train"]```, not under ```metadata["train"][self.config.languages[0]]```

same for audio urls

### Steps to reproduce the bug

```
from datasets import load_dataset

dataset = load_dataset("facebook/voxpopuli","en")
```

### Expected behavior

Dataset should be loaded successfully.

### Environment info

- `datasets` version: 2.19.0
- Platform: Linux-5.15.0-1041-aws-x86_64-with-glibc2.31
- Python version: 3.10.13
- `huggingface_hub` version: 0.22.2
- PyArrow version: 16.0.0
- Pandas version: 2.2.0
- `fsspec` version: 2023.12.2