R600/SI: Minor cleanup of function

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219616 91177308-0d34-0410-b5e6-96231b3b80d8
Fix a broadcast related regression on the vector shuffle lowering.

Summary: Test by Robert Lougher!

Reviewers: chandlerc

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D5745

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219617 91177308-0d34-0410-b5e6-96231b3b80d8