[Mips] Fix expsensive_check test failure when x86 run readcyclecounter.ll

Fix pr llvm#127553

Author: yingopq

llvm/lib/Target/Mips/MipsRegisterInfo.cpp

@@ -205,6 +205,7 @@ getReservedRegs(const MachineFunction &MF) const {
 
   // Reserve hardware registers.
   Reserved.set(Mips::HWR29);
+  Reserved.set(Mips::HWR2);
 
   // Reserve DSP control register.
   Reserved.set(Mips::DSPPos);