AMDGPU: Make getNamedOperandIdx declaration readonly

This matches how it is defined in the generated implementation.

llvm-svn: 248598

llvm/lib/Target/AMDGPU/AMDGPUInstrInfo.h

@@ -196,6 +196,7 @@ public:
 };
 
 namespace AMDGPU {
+  LLVM_READONLY
   int16_t getNamedOperandIdx(uint16_t Opcode, uint16_t NamedIndex);
 }  // End namespace AMDGPU
 

llvm/lib/Target/AMDGPU/SIInstrInfo.h

@@ -338,8 +338,10 @@ public:
 
   /// \brief Returns the operand named \p Op.  If \p MI does not have an
   /// operand named \c Op, this function returns nullptr.
+  LLVM_READONLY
   MachineOperand *getNamedOperand(MachineInstr &MI, unsigned OperandName) const;
 
+  LLVM_READONLY
   const MachineOperand *getNamedOperand(const MachineInstr &MI,
                                         unsigned OpName) const {
     return getNamedOperand(const_cast<MachineInstr &>(MI), OpName);