[bark] fix loading of generation config

[gante]

What does this PR do?

Supercedes #36570

BarkModel.can_generate() is False, but it needs to be True. Explanation in the diff.

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Reproducer of the issue:

from transformers import pipeline

pipe = pipeline("text-to-speech", "suno/bark")
pipe("hello")

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[SunMarc]

Nice !