aco: apply NUW to additions for scratch access

aco: apply NUW to additions for scratch access

fossil-db (navi21):
Totals from 52 (0.04% of 135636) affected shaders:
Instrs: 79036 -> 78567 (-0.59%)
CodeSize: 431188 -> 427984 (-0.74%)
Latency: 1318142 -> 1313821 (-0.33%)
InvThroughput: 293842 -> 292836 (-0.34%)
VClause: 2555 -> 2361 (-7.59%); split: -8.06%, +0.47%
Copies: 8746 -> 8767 (+0.24%); split: -0.11%, +0.35%

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20117>