[RISCV] Prune unnecessary LMUL from SiFive sf.vfwmacc.4x4x4 pseudo instruction. NFC

We had an LMUL=8 pseudo, but this instruction has result EMUL=LMUL*2
like a standard widening instruction.

Author: topperc

llvm/lib/Target/RISCV/RISCVInstrInfoXSf.td

@@ -391,7 +391,7 @@ multiclass VPseudoSiFiveVQMACCQOQ {
 }
 
 multiclass VPseudoSiFiveVFWMACC {
-  foreach m = MxListVF2 in
+  foreach m = MxListFW in
     let VLMul = m.value in
     defm NAME : VPseudoSiFiveVMACC<m.MX, m.wvrclass, m.vrclass>;
 }