[mlir][MemRef] Fix the simplification of extract_strided_metadata(subview)

Prior to this patch we were wrongly applying the sub-strides to the
computation of the final offset of the subview.

Put differently, we were computing the offset as:
```
offset = baseOffset + sum(subOffset#i * baseStrides#i * subSizes#i)
```
Whereas we should be doing:
```
offset = baseOffset + sum(subOffset#i * baseStrides#i)
```
I.e., drop the subSizes#i term from the sum.

Differential Revision: https://reviews.llvm.org/D136107