Fix warnings about unused varibles on builds without asserts.

Author: kosarev

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

@@ -6256,13 +6256,11 @@ LegalizerHelper::LegalizeResult LegalizerHelper::lowerFPTOSI(MachineInstr &MI) {
 LegalizerHelper::LegalizeResult
 LegalizerHelper::lowerFPTRUNC_F64_TO_F16(MachineInstr &MI) {
   const LLT S1 = LLT::scalar(1);
-  const LLT S16 = LLT::scalar(16);
   const LLT S32 = LLT::scalar(32);
-  const LLT S64 = LLT::scalar(64);
 
   auto [Dst, Src] = MI.getFirst2Regs();
-  assert(MRI.getType(Dst).getScalarType() == S16 &&
-         MRI.getType(Src).getScalarType() == S64);
+  assert(MRI.getType(Dst).getScalarType() == LLT::scalar(16) &&
+         MRI.getType(Src).getScalarType() == LLT::scalar(64));
 
   if (MRI.getType(Src).isVector()) // TODO: Handle vectors directly.
     return UnableToLegalize;