[MLIR] Simplify division extraction unit testing.

The new `getLocalReprs` function also outputs `dividends` and
`denominators` and hence the CheckDivisionRepresentation fn is
modified to take the newer getLocalReprs function into account.

Signed-off-by: Prashant Kumar <pk5561@gmail.com>

Reviewed By: Groverkss

Differential Revision: https://reviews.llvm.org/D115146