[VENTUS][RISCV][fix] Fix the undefined physical register bug

Fix the undefined physical register bug when inserting VMV_V_X instruction
in "checkJoinMBB" funtion to compile with "--verify-machineinstr" parameter.

llvm/lib/Target/RISCV/VentusInsertJoinToVBranch.cpp

@@ -269,6 +269,7 @@ bool VentusInsertJoinToVBranch::checkJoinMBB(MachineBasicBlock &MBB) const {
       }
       if (NeedToBeErased) {
         IsChanged |= true;
+        MBB.addLiveIn(MCRegister(MI.getOperand(0).getReg()));
         MI.eraseFromParent();
       }
     }