Ensure a scalar pointer when issuing a vector load

Even tough we may want to generate a vector load, the address from which to load
still is a scalar. Make sure even if previous address computations may have been
vectorized, that the addresses are also available as scalars.

This fixes http://llvm.org/PR19469

Reported-by:  Jeremy Huddleston Sequoia <jeremyhu@apple.com>

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@206510 91177308-0d34-0410-b5e6-96231b3b80d8