R600: LDS instructions shouldn't implicitly define OQAP

LDS instructions are pseudo instructions which model
the OQAP defs and uses within a single instruction.

This fixes a hang in the opencv MedianFilter tests.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203818 91177308-0d34-0410-b5e6-96231b3b80d8