UPSTREAM: nir/lower_io_to_vector: fix per vertex io handling for arrays

The pass was processing the per vertex index from the wrong end
of the array deref chain.

(cherry picked from commit 8b180ab98b9
 https://gitlab.freedesktop.org/mesa/mesa.git main)

BUG=b:177028255
TEST=CtsDeqp on volteer

Fixes: bcd14756eec8 ("nir/lower_io_to_vector: add flat mode")

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10798>
Change-Id: I8c90c830acf61690b5d8c4e940997e7c790b15a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/mesa/+/2986081
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Ilja H. Friedel <ihf@chromium.org>
Commit-Queue: Ilja H. Friedel <ihf@chromium.org>
Tested-by: Ilja H. Friedel <ihf@chromium.org>
1 file changed