[RISCV] Use isVLPreservingConfig in isConvertibleToVMV_V_V. NFC

Author: topperc

llvm/lib/Target/RISCV/RISCVInstrInfo.cpp

@@ -293,11 +293,7 @@ static bool isConvertibleToVMV_V_V(const RISCVSubtarget &STI,
         }
         // Only permit `vsetvli x0, x0, vtype` between COPY and the source
         // define instruction.
-        if (MBBI->getOperand(0).getReg() != RISCV::X0)
-          return false;
-        if (MBBI->getOperand(1).isImm())
-          return false;
-        if (MBBI->getOperand(1).getReg() != RISCV::X0)
+        if (!RISCVInstrInfo::isVLPreservingConfig(*MBBI))
           return false;
         continue;
       }