Fix test_model_parallelization
# What does this PR do?

When number of gpus is greater than ```len(model.device_map.keys())```, exceptional case happens.

Fixes #17248


## Who can review?

@patrickvonplaten

_The documentation is not available anymore as the PR was closed or merged._<|||||>Change is fine by me! @sgugger @stas00 what do you think? 