[RISCV] Minor style cleanup to cf17a24 [nfc]

This was suggested in another related review, so backporting it to the
existing code as well.

Author: preames

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -7920,8 +7920,7 @@ SDValue RISCVTargetLowering::lowerEXTRACT_VECTOR_ELT(SDValue Op,
     MVT M1VT = getLMUL1VT(ContainerVT);
     unsigned OrigIdx = IdxC->getZExtValue();
     EVT ElemVT = VecVT.getVectorElementType();
-    unsigned ElemSize = ElemVT.getSizeInBits().getKnownMinValue();
-    unsigned ElemsPerVReg = MinVLen / ElemSize;
+    unsigned ElemsPerVReg = MinVLen / ElemVT.getFixedSizeInBits();
     unsigned RemIdx = OrigIdx % ElemsPerVReg;
     unsigned SubRegIdx = OrigIdx / ElemsPerVReg;
     unsigned ExtractIdx =