[RISCV] Fix -Wunused-variable in release builds. NFCI

[alexfh]

Summary

Fix -Wunused-variable in release builds

llvm/lib/Target/RISCV/RISCVExpandPseudoInsts.cpp

bool RISCVExpandPseudo::expandRV32ZdinxStore(MachineBasicBlock &MBB,
   Register Lo = TRI->getSubReg(MBBI->getOperand(0).getReg(), RISCV::sub_32);
   Register Hi = TRI->getSubReg(MBBI->getOperand(0).getReg(), RISCV::sub_32_hi);
   BuildMI(MBB, MBBI, DL, TII->get(RISCV::SW))
       .addReg(Lo, getKillRegState(MBBI->getOperand(0).isKill()))
       .addReg(MBBI->getOperand(1).getReg())
       .add(MBBI->getOperand(2));
   if (MBBI->getOperand(2).isGlobal() || MBBI->getOperand(2).isCPI()) {
     // FIXME: Zdinx RV32 can not work on unaligned scalar memory.
-    const auto &STI = MF->getSubtarget<RISCVSubtarget>();
-    assert(!STI.enableUnalignedScalarMem());
+    assert(!MF->getSubtarget<RISCVSubtarget>().enableUnalignedScalarMem());
 
     assert(MBBI->getOperand(2).getOffset() % 8 == 0);
     MBBI->getOperand(2).setOffset(MBBI->getOperand(2).getOffset() + 4);
     BuildMI(MBB, MBBI, DL, TII->get(RISCV::SW))
         .addReg(Hi, getKillRegState(MBBI->getOperand(0).isKill()))
         .add(MBBI->getOperand(1))
         .add(MBBI->getOperand(2));
   } else {