This change switches from `ult` to `slt` in the comparison generated by
`TileLoadOpWithMaskAndPadNonZeroConversion`.
From the updated test:
```
%[[ROW_IS_ACTIVE:.*]] = arith.cmpi slt, %[[TILE_SLICE_INDEX]], %[[NUM_ROWS]] : index
```
Here:
- `%[[TILE_SLICE_INDEX]]` is always non-negative.
- `%[[NUM_ROWS]]` represents the number of remaining rows.
`%[[NUM_ROWS]]` is computed as:
```mlir
%c-4 = arith.constant -4 : index
%c-4_vscale = arith.muli %c-4, %vscale_11 : index
%num_rows_remaining = arith.addi %num_rows_init, %c-4_vscale : index
```
(inserted by the "arm-sme-vector-legalization" pass, see
`VectorLegalization.cpp`).
Because of the subtraction, `%num_rows_remaining` can be negative.
Therefore, the comparison must be signed (`slt`) rather than unsigned
(`ult`).
Fixes: https://github.com/iree-org/iree/issues/21714
e59414f9bf