Fixing RotaryEmbedding.forward to return float16 values in float16 precision mode.
# What does this PR do?

RotaryEmbedding.forward() returns values with float32 precision even in float16 precision mode.
This affects to the subsequent calculation and takes extra GPU memory usage.
This PR fixes that problem.


Fixes #24261


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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      Pull Request section?
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      to it if that's the case.
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      [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?



I will investigate whether or not this is the source of instabilities in Llama2! If so, will adresse it