[X86] Silence an unused-variable warning (NFC)

/llvm-project/llvm/lib/Target/X86/GISel/X86InstructionSelector.cpp:1054:9:
 error: unused variable 'RhsBank' [-Werror,-Wunused-variable]
  auto *RhsBank = RBI.getRegBank(RhsReg, MRI, TRI);
        ^
1 error generated.

Author: DamonFool

llvm/lib/Target/X86/GISel/X86InstructionSelector.cpp

@@ -1051,7 +1051,7 @@ bool X86InstructionSelector::selectFCmp(MachineInstr &I,
   assert((LhsReg.isVirtual() && RhsReg.isVirtual()) &&
          "Both arguments of FCMP need to be virtual!");
   auto *LhsBank = RBI.getRegBank(LhsReg, MRI, TRI);
-  auto *RhsBank = RBI.getRegBank(RhsReg, MRI, TRI);
+  [[maybe_unused]] auto *RhsBank = RBI.getRegBank(RhsReg, MRI, TRI);
   assert((LhsBank == RhsBank) &&
          "Both banks assigned to FCMP arguments need to be same!");