[SCEV] Swap order of arguments to MatchBinaryAddToConst (NFCI). (#91945)

The argument order to MatchBinaryAddToConst doesn't match the comment
and also is counter-intuitive (passing RHS before LHS, C2 before C1).

This patch adjusts the order to be inline with the calls above, which
should be equivalent, but more natural:
https://alive2.llvm.org/ce/z/ZWGp-Z

PR: https://github.com/llvm/llvm-project/pull/91945