[LoopSimplify] Improve a test for loop simplify minorly. NFC.

I did some basic testing while looking for a bug in my recent change to
loop simplify and even though it didn't find the bug it seems like
a useful improvement anyways.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306256 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed