[kernels] Fix XPU layernorm kernel (#41583)
* fix
* add comment
* better fix
* style
* Update src/transformers/modeling_utils.py
Co-authored-by: Marc Sun <57196510+SunMarc@users.noreply.github.com>
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Co-authored-by: Marc Sun <57196510+SunMarc@users.noreply.github.com>
