[mlir][vector] Fix off-by-one error in `getTransferChunkAccessed` (#70292)

If a dimension does not appear in the permutation map of a vector
transfer op, the size of the accessed slice in that dimension is `1`.
Before this fix, `getTransferChunkAccessed` used to return `0` for such
dimensions, which would means that `0` elements in the underlying
tensor/memref are accessed.

Note: There is no test case that fails due to this bug and because this
interface method is currently only used in one place, it is hard to
write a regression test. This fix is in preparation of subset hoisting
functionality that will be added in subsequent commits.