[mlir][tosa] Fix crash when inferring shape of tosa.equal

The tosa-infer-shapes pass crashes when trying to infer the output shape
of tosa.equal when the input shape is unranked.
This is due to tosa-infer-shapes requiring at least information on the
base type of the resulting operation from inferReturnTypeComponents.
This change enhances EqualOp::inferReturnTypeComponents to always supply
the inferred elementType.

Reviewed By: eric-k256

Differential Revision: https://reviews.llvm.org/D149582