aco: don't move descriptor loads below buffer loads

aco: don't move descriptor loads below buffer loads

fossil-db (GFX10.3):
Totals from 52870 (36.15% of 146267) affected shaders:
VGPRs: 2109936 -> 2110056 (+0.01%); split: -0.01%, +0.01%
CodeSize: 134898056 -> 134812748 (-0.06%); split: -0.08%, +0.02%
MaxWaves: 1347354 -> 1347346 (-0.00%)
Instrs: 25598063 -> 25575415 (-0.09%); split: -0.11%, +0.02%
Latency: 432491613 -> 432047723 (-0.10%); split: -0.12%, +0.02%
InvThroughput: 90940977 -> 90927545 (-0.01%); split: -0.03%, +0.01%
VClause: 570039 -> 570019 (-0.00%); split: -0.05%, +0.04%
SClause: 1145076 -> 1139040 (-0.53%); split: -0.60%, +0.07%
Copies: 1513949 -> 1513102 (-0.06%); split: -0.32%, +0.26%
Branches: 524279 -> 524275 (-0.00%); split: -0.03%, +0.03%

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/6489>