[GlobalISel] Remove unused MF from lambda captures (NFC).

[fhahn]

Summary

Caught by a warning when building with recent versions of clang

[arphaman]

Looks like it's fixed by r311781

[fhahn]

Yep it's fixed by that commit, thanks for catching that.

lib/CodeGen/GlobalISel/LegalizerHelper.cpp

case TargetOpcode::G_GEP: {
     assert(TypeIdx == 1 && "unable to legalize pointer of GEP");
     unsigned OffsetExt = MRI.createGenericVirtualRegister(WideTy);
     MIRBuilder.buildSExt(OffsetExt, MI.getOperand(2).getReg());
     MI.getOperand(2).setReg(OffsetExt);
     return Legalized;
   }
   case TargetOpcode::G_PHI: {
     assert(TypeIdx == 0 && "Expecting only Idx 0");
-    MachineFunction *MF = MI.getParent()->getParent();
-    auto getExtendedReg = [this, MF, WideTy](unsigned Reg,
-                                             MachineBasicBlock &MBB) {
+    auto getExtendedReg = [this, WideTy](unsigned Reg,
       auto FirstTermIt = MBB.getFirstTerminator();
       MIRBuilder.setInsertPt(MBB, FirstTermIt);
       MachineInstr *DefMI = MRI.getVRegDef(Reg);
       MachineInstrBuilder MIB;
       if (DefMI->getOpcode() == TargetOpcode::G_TRUNC)
         MIB = MIRBuilder.buildAnyExtOrTrunc(WideTy,
                                             DefMI->getOperand(1).getReg());
       else