DeadCodeElim: Compute correct liveout for non-affine accesses

Thanks to Johannes Doerfert for narrowing down the bug.

Reported-by: Chris Jenneisch <chrisj@codeaurora.org>

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@212796 91177308-0d34-0410-b5e6-96231b3b80d8