[VE][NFC] Fix use-after-free in VEInstrInfo

First call getOperand, then erase the MachineInstr. Not the other way
round.

Expected to fix test/CodeGen/VE/VELIntrinsics/lvm.ll

Detected by asan buildbot:

  sanitizer-x86_64-linux-fast
  (https://lab.llvm.org/buildbot/#/builders/5/builds/15384)

llvm/lib/Target/VE/VEInstrInfo.cpp

@@ -942,11 +942,11 @@ bool VEInstrInfo::expandPostRAPseudo(MachineInstr &MI) const {
     MachineInstrBuilder MIB =
         BuildMI(*MBB, MI, DL, get(VE::SVMmi), Dest).addReg(VMZ).addImm(Imm);
     MachineInstr *Inst = MIB.getInstr();
-    MI.eraseFromParent();
     if (KillSrc) {
       const TargetRegisterInfo *TRI = &getRegisterInfo();
       Inst->addRegisterKilled(MI.getOperand(1).getReg(), TRI, true);
     }
+    MI.eraseFromParent();
     return true;
   }
   case VE::VFMKyal: