[RISCV] Use frmarg instead of ixlenimm in PseudoFROUND. NFC (llvm#171563)

This is expanded with a custom inserter and this immediate will be
copied to the frm operand of a non-pseudo instruction.

Author: topperc

llvm/lib/Target/RISCV/RISCVInstrInfoF.td

@@ -316,7 +316,7 @@ multiclass FPCmp_rr_m<bits<7> funct7, bits<3> funct3, string opcodestr,
 }
 
 class PseudoFROUND<DAGOperand Ty, ValueType vt, ValueType intvt = XLenVT>
-    : Pseudo<(outs Ty:$rd), (ins Ty:$rs1, Ty:$rs2, ixlenimm:$rm),
+    : Pseudo<(outs Ty:$rd), (ins Ty:$rs1, Ty:$rs2, frmarg:$rm),
       [(set Ty:$rd, (vt (riscv_fround Ty:$rs1, Ty:$rs2, (intvt timm:$rm))))]> {
   let hasSideEffects = 0;
   let mayLoad = 0;