[PM] Fix a contradiction in the comments noticed by Anders.

Have I mentioned that functions returning true on error and false on
success are confusing? They're more confusing when their name is
"verify". Anyways...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199622 91177308-0d34-0410-b5e6-96231b3b80d8