Fix `memref.expand_shape` verifier (#91501)

Torch-mlir integration is currently blocked on `memref.expand_shape`
verifier errors of the form

```
'memref.expand_shape' op invalid output shape provided at pos 1
```

The verifier code generating these errors was introduced in
https://github.com/llvm/llvm-project/pull/91245. I have commented there
why I believe it's incorrect. This PR has my suggested fix.

Unfortunately, this does not seem to be directly testable on `memref`
IR, because `static_output_shape` is not directly exposed in the custom
assembly format.