R600: Remove some dead code from the AMDILCFGStructurizer

Reviewed-by: Vincent Lejeune<vljn at ovi.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192812 91177308-0d34-0410-b5e6-96231b3b80d8
R600: Fix a crash in the AMDILCFGStructurizer

We were calling llvm_unreachable() when failing to optimize the
branch into if case.  However, it is still possible for us
to structurize the CFG by duplicating blocks even if this optimization
fails.

Reviewed-by: Vincent Lejeune<vljn at ovi.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192813 91177308-0d34-0410-b5e6-96231b3b80d8