[CodeGen] Avoid access after runtime

Insts must be destroyd before xParent
or it can read it with stack like this:
   0 in llvm::MachineInstr::getMF() const MachineInstr.cpp:637:3
   1 in getMF MachineInstr.h:302:50
   2 in removeNodeFromList MachineBasicBlock.cpp:163:32