Fix whisper and speech to text doc 
# What does this PR do?
Previously the documentation was badly indented for both models and indicated that
> If `decoder_input_ids` and `decoder_inputs_embeds` are both unset, `decoder_inputs_embeds` takes the value of `inputs_embeds`.`
Which is on valid for the forward pass of the `ForConditionnalGeneration` not for the model alone. 
_The documentation is not available anymore as the PR was closed or merged._