Adapt find_tied_parameters to handle breaking change in Accelerate
# What does this PR do?

In the upcoming version of Accelerate, `find_tied_parameters` returns a list of list instead of dictionary. While there is a hack in place to make sure the code in Transformers keeps working, it is a hack so it would be best to change the way we handle the result of `find_tied_parameters`.

This PR does just that.
_The documentation is not available anymore as the PR was closed or merged._