Fix Wdocumentation warning. NFC.

warning: '\returns' command used in a comment that is attached to a function returning void

Author: RKSimon

llvm/lib/Target/AMDGPU/MCTargetDesc/SIMCCodeEmitter.cpp

@@ -49,7 +49,6 @@ class SIMCCodeEmitter : public  AMDGPUMCCodeEmitter {
                          SmallVectorImpl<MCFixup> &Fixups,
                          const MCSubtargetInfo &STI) const override;
 
-  /// \returns the encoding for an MCOperand.
   void getMachineOpValue(const MCInst &MI, const MCOperand &MO, APInt &Op,
                          SmallVectorImpl<MCFixup> &Fixups,
                          const MCSubtargetInfo &STI) const override;