Simplify dtype instantiation

[Cyrilvallez]

What does this PR do?

As per the title. Cleanu-up a bit after #42805 and in general

[HuggingFaceDocBuilderDev]

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[ArthurZucker]

    @property
    def dtype(self) -> torch.dtype:
        """
        `torch.dtype`: The dtype of the module (assuming that all the module parameters have the same dtype).
        """
        dtype = self._dtype or next(param.dtype for param in self.parameters() if param.is_floating_point())
        if isinstance(dtype, str):
            if hasattr(torch, dtype):
                dtype = getattr(torch, dtype)
        return dtype

you did not change this one either no

[Cyrilvallez]

I did, it's here haha