R600/SI: Fix trailing comma with modifiers

Instructions with 1 operand can still use source modifiers,
so make sure we don't print an extra comma afterwards.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226226 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed