[RISCV] Use MVT::changeVectorElementType. NFC

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Differential Revision: https://phabricator.intern.facebook.com/D60251428

Author: topperc

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -8273,11 +8273,9 @@ SDValue RISCVTargetLowering::lowerVectorTruncLike(SDValue Op,
         getDefaultVLOps(SrcVT, ContainerVT, DL, DAG, Subtarget);
   }
 
-  LLVMContext &Context = *DAG.getContext();
-  const ElementCount Count = ContainerVT.getVectorElementCount();
   do {
     SrcEltVT = MVT::getIntegerVT(SrcEltVT.getSizeInBits() / 2);
-    EVT ResultVT = EVT::getVectorVT(Context, SrcEltVT, Count);
+    MVT ResultVT = ContainerVT.changeVectorElementType(SrcEltVT);
     Result = DAG.getNode(RISCVISD::TRUNCATE_VECTOR_VL, DL, ResultVT, Result,
                          Mask, VL);
   } while (SrcEltVT != DstEltVT);