AMDGPU: Add m0 vgpr load loop block as successor

This shows up as a verifier error when I move this
earlier, not sure why it didn't before.

llvm-svn: 274275

llvm/lib/Target/AMDGPU/SILowerControlFlow.cpp

@@ -521,6 +521,7 @@ bool SILowerControlFlow::loadM0(MachineInstr &MI, MachineInstr *MovRel, int Offs
   // Move the rest of the block into a new block.
   RemainderBB->transferSuccessors(&MBB);
   RemainderBB->splice(RemainderBB->begin(), &MBB, I, MBB.end());
+  MBB.addSuccessor(LoopBB);
 
   emitLoadM0FromVGPRLoop(*LoopBB, DL, MovRel, *Idx, Offset);