Instead of avoiding out-of-bounds access, avoid creating a load larger
than the original attribute. This should work just as well, since the only
situations expending a load helped was because we shrunk it first.

Also fixes a bug where a 3 component load (4 components with the first
component skipped) would be incorrectly expanded to 4 components because
the stride check would never be performed. Maybe we should avoid skipping
the first component in some situations, but I'm not sure if it's worth
the VGPR cost.

fossil-db (vega10):
Totals from 583 (0.39% of 149974) affected shaders:
CodeSize: 1496848 -> 1500868 (+0.27%); split: -0.03%, +0.30%
Instrs: 286155 -> 286575 (+0.15%); split: -0.07%, +0.22%
Latency: 2947101 -> 2946865 (-0.01%); split: -0.23%, +0.22%
InvThroughput: 797396 -> 797127 (-0.03%); split: -0.08%, +0.04%

fossil-db (polaris10):
Totals from 583 (0.39% of 151365) affected shaders:
SGPRs: 38880 -> 39216 (+0.86%)
VGPRs: 24440 -> 24356 (-0.34%)
CodeSize: 1506808 -> 1510876 (+0.27%); split: -0.01%, +0.28%
Instrs: 288735 -> 289167 (+0.15%); split: -0.06%, +0.21%
Latency: 2963263 -> 2961884 (-0.05%); split: -0.24%, +0.19%
InvThroughput: 802351 -> 801665 (-0.09%); split: -0.12%, +0.04%

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <mesa/mesa!9007>