[mlir][memref] Use current source type in getCanonicalSubViewResultType.

Use the current instead of the new source type to compute the rank-reduction map in getCanonicalSubViewResultType. Otherwise, the computation of the rank-reduction map fails when folding a cast into a subview since the strides of the new source type cannot be related to the strides of the current result type.

Depends On D115428

Reviewed By: nicolasvasilache

Differential Revision: https://reviews.llvm.org/D115446