pre-RA-sched: fix TargetOpcode usage

TargetOpcodes need to be treaded as Machine- and not ISD-Opcodes.

Signed-off-by: Christian König <christian.koenig@amd.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177518 91177308-0d34-0410-b5e6-96231b3b80d8