Fix doc examples: 'CausalLMOutput...' object has no attribute 'last_hidden_state'
# What does this PR do?

In some doc examples, the line

```
last_hidden_states = outputs.last_hidden_state
```

will fail when the return value if of type `CausalLMOutput...` (e.g. `CausalLMOutputWithCrossAttentions`).

This PR fixes these lines by using

```
logits = outputs.logits
```

## Who can review

@patrickvonplaten 
Awesome!