[test] Fix scev-expander-preserve-lcssa.ll under NPM

The NPM runs loop passes over loops in forward program order, rather
than the legacy loop PM's reverse program order. This seems to produce
better results as shown here.

I verified that changing the loop order to reverse program order results
in the same IR with the NPM.

Reviewed By: fhahn

Differential Revision: https://reviews.llvm.org/D92817