[RISCV] Use RISCVSubtarget to get XLen in CC_RISCV. NFC

Author: topperc

llvm/lib/Target/RISCV/RISCVCallingConv.cpp

@@ -255,9 +255,8 @@ bool llvm::CC_RISCV(unsigned ValNo, MVT ValVT, MVT LocVT,
   const RISCVSubtarget &Subtarget = MF.getSubtarget<RISCVSubtarget>();
   const RISCVTargetLowering &TLI = *Subtarget.getTargetLowering();
 
-  unsigned XLen = DL.getLargestLegalIntTypeSizeInBits();
-  assert(XLen == 32 || XLen == 64);
-  MVT XLenVT = XLen == 32 ? MVT::i32 : MVT::i64;
+  unsigned XLen = Subtarget.getXLen();
+  MVT XLenVT = Subtarget.getXLenVT();
 
   // Static chain parameter must not be passed in normal argument registers,
   // so we assign t2 for it as done in GCC's __builtin_call_with_static_chain