Parenthesis on xpu_available

[muellerzr]

What does this PR do?

This existed before the refactor, but we are missing parenthesis around one of the calls to is_xpu_available

Fixes #2637

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@BenjaminBossan

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[BenjaminBossan]

Thanks, LGTM.

Would be nice if the linter could catch this, checking bool on a function is probably unintended 99.99% of the time.