move device statements outside if statements
Author: e-yi
Pull request: yes

# What does this PR do?

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Move some device statements outside if statements.

There are three model classes (GPT2Model, GPTNeoModel, CTRLModel) that state the variable `device` inside a `if` statement in their `forward()` method. This may lead to some inconvenience for GPT2Model #11179, and is not consistent with the way it is written in other model classes.

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- [ ] Did you write any new necessary tests?


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@LysandreJik 

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