[RISCV][NFC] Use TargetRegisterClass::hasSubClassEq in storeRegToStackSlot/loadReadFromStackSlot

Simply checking for register class equality will break once additional 
register classes are added (as is done for the RVC instruction set extension).

llvm-svn: 320036
diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfo.cpp b/llvm/lib/Target/RISCV/RISCVInstrInfo.cpp
index 5b4f4fc..186fe36 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfo.cpp
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfo.cpp
@@ -52,7 +52,7 @@
   if (I != MBB.end())
     DL = I->getDebugLoc();
 
-  if (RC == &RISCV::GPRRegClass)
+  if (RISCV::GPRRegClass.hasSubClassEq(RC))
     BuildMI(MBB, I, DL, get(RISCV::SW))
         .addReg(SrcReg, getKillRegState(IsKill))
         .addFrameIndex(FI)
@@ -70,7 +70,7 @@
   if (I != MBB.end())
     DL = I->getDebugLoc();
 
-  if (RC == &RISCV::GPRRegClass)
+  if (RISCV::GPRRegClass.hasSubClassEq(RC))
     BuildMI(MBB, I, DL, get(RISCV::LW), DstReg).addFrameIndex(FI).addImm(0);
   else
     llvm_unreachable("Can't load this register from stack slot");