nir/load_store_vectorize: don't ignore subgroup memory barriers

Not sure why I thought this was correct, but we should consider them for
optimization purposes.

Fixes: ce9205c03bd ('nir: add a load/store vectorization pass')
Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4202>
(cherry picked from commit f4eb833a12523142d908bf67e08904f4e8a866e9)
2 files changed