[mlir] Lookup the latest value with a legal type when remapping values.

The current condition implies that the target materialization will be
called even if the type is the new operand type is legal, but slightly
different. For example, if there is a bufferization pattern that changes
memref layout, then target materialization for an illegal type
(TensorType) would be called.

Differential Revision: https://reviews.llvm.org/D93126