exclude mutated buffer (#2876)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/2876

Fixing the tag constant for mutable buffer. The buffer shouldn't be tagged if it's going to be mutated by the delegated. It's more common in hardware backends

Will follow up and test having delegate consume mutation

Reviewed By: mcr229, angelayi

Differential Revision: D55812844

fbshipit-source-id: e0be4c2dc295141d673cccb1aeecee45894b1e70