remove redundant to_dtype in Fused Schedular Nodes (#118365)
Fix https://github.com/pytorch/pytorch/issues/115260.
This issue is triggered by `FusedSchedularNodes` cases.
We always store `lowp buffer` to `store_cache` then load `lowp buffer` from `store_cache` and `convert it to float` before `compute ops`.
Now we will generate a `{key: to(float32)_expr, value: the float32 cse var before to_dtype and store}` in `cse.cache`.
Then the `to_dtype(float32)` after `load` will hit this cache and not generate a new var with cast codes.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/118365
Approved by: https://github.com/jgong5, https://github.com/jansel
