radv,aco: lower vulkan_resource_index in NIR

radv,aco: lower vulkan_resource_index in NIR

fossil-db (Sienna Cichlid):
Totals from 31338 (19.31% of 162293) affected shaders:
MaxWaves: 758634 -> 758616 (-0.00%)
Instrs: 26398289 -> 26378282 (-0.08%); split: -0.09%, +0.01%
CodeSize: 141048208 -> 140971060 (-0.05%); split: -0.07%, +0.01%
VGPRs: 1373656 -> 1373736 (+0.01%)
SpillSGPRs: 9944 -> 9924 (-0.20%); split: -0.24%, +0.04%
SpillVGPRs: 1892 -> 1898 (+0.32%); split: -0.95%, +1.27%
Latency: 308570144 -> 308528462 (-0.01%); split: -0.03%, +0.02%
InvThroughput: 57698072 -> 57684901 (-0.02%); split: -0.07%, +0.04%
VClause: 440357 -> 440602 (+0.06%); split: -0.02%, +0.08%
SClause: 974724 -> 973315 (-0.14%); split: -0.18%, +0.04%
Copies: 1944925 -> 1945103 (+0.01%); split: -0.11%, +0.12%
Branches: 799444 -> 799461 (+0.00%); split: -0.00%, +0.00%
PreSGPRs: 1619860 -> 1619233 (-0.04%); split: -0.05%, +0.02%
PreVGPRs: 1252813 -> 1252863 (+0.00%); split: -0.00%, +0.00%

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12773>