nir: Use nir_deref_mode_may_be in deref optimizations

All the checks being replaced are fore potential aliasing so we want to
flush stores whenever the mode might be something that aliases.

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6332>
3 files changed