[Sanitizer] Try to fix infinite loop in frame pointer unwinder

Using > instead of >= ensures that each frame deref makes progress and
that we eventually terminate.

Issue: https://code.google.com/p/address-sanitizer/issues/detail?id=162

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@175661 91177308-0d34-0410-b5e6-96231b3b80d8