mem: Remove CoherentBus snoop port unused private member
mem: Remove CoherentBus snoop port unused private member

This patch removes an unused member to avoid getting compiler warnings
when using clang.

qizenguf/MLC-STT,TUD-OS/gem5-dtu,gem5/gem5,KuroeKurose/gem5,sobercoder/gem5,cancro7/gem5,KuroeKurose/gem5,TUD-OS/gem5-dtu,austinharris/gem5-riscv,yb-kim/gemV,gedare/gem5,cancro7/gem5,yb-kim/gemV,kaiyuanl/gem5,samueldotj/TeeRISC-Simulator,yb-kim/gemV,rallylee/gem5,rallylee/gem5,rjschof/gem5,zlfben/gem5,KuroeKurose/gem5,aclifton/cpeg853-gem5,SanchayanMaity/gem5,austinharris/gem5-riscv,briancoutinho0905/2dsampling,powerjg/gem5-ci-test,yb-kim/gemV,Weil0ng/gem5,HwisooSo/gemV-update,SanchayanMaity/gem5,aclifton/cpeg853-gem5,gem5/gem5,HwisooSo/gemV-update,austinharris/gem5-riscv,samueldotj/TeeRISC-Simulator,SanchayanMaity/gem5,HwisooSo/gemV-update,qizenguf/MLC-STT,KuroeKurose/gem5,sobercoder/gem5,rallylee/gem5,kaiyuanl/gem5,gem5/gem5,sobercoder/gem5,powerjg/gem5-ci-test,cancro7/gem5,gem5/gem5,powerjg/gem5-ci-test,qizenguf/MLC-STT,markoshorro/gem5,rallylee/gem5,qizenguf/MLC-STT,briancoutinho0905/2dsampling,Weil0ng/gem5,samueldotj/TeeRISC-Simulator,HwisooSo/gemV-update,aclifton/cpeg853-gem5,kaiyuanl/gem5,powerjg/gem5-ci-test,markoshorro/gem5,gedare/gem5,Weil0ng/gem5,aclifton/cpeg853-gem5,qizenguf/MLC-STT,Weil0ng/gem5,zlfben/gem5,yb-kim/gemV,austinharris/gem5-riscv,rjschof/gem5,TUD-OS/gem5-dtu,KuroeKurose/gem5,yb-kim/gemV,samueldotj/TeeRISC-Simulator,HwisooSo/gemV-update,austinharris/gem5-riscv,cancro7/gem5,zlfben/gem5,zlfben/gem5,Weil0ng/gem5,cancro7/gem5,KuroeKurose/gem5,qizenguf/MLC-STT,rallylee/gem5,powerjg/gem5-ci-test,austinharris/gem5-riscv,KuroeKurose/gem5,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,kaiyuanl/gem5,rjschof/gem5,markoshorro/gem5,cancro7/gem5,gedare/gem5,gedare/gem5,rjschof/gem5,TUD-OS/gem5-dtu,rjschof/gem5,rallylee/gem5,HwisooSo/gemV-update,briancoutinho0905/2dsampling,yb-kim/gemV,markoshorro/gem5,sobercoder/gem5,zlfben/gem5,Weil0ng/gem5,markoshorro/gem5,samueldotj/TeeRISC-Simulator,SanchayanMaity/gem5,aclifton/cpeg853-gem5,powerjg/gem5-ci-test,cancro7/gem5,markoshorro/gem5,gedare/gem5,sobercoder/gem5,gem5/gem5,aclifton/cpeg853-gem5,rjschof/gem5,briancoutinho0905/2dsampling,zlfben/gem5,HwisooSo/gemV-update,sobercoder/gem5,kaiyuanl/gem5,gedare/gem5,SanchayanMaity/gem5,kaiyuanl/gem5,briancoutinho0905/2dsampling,gem5/gem5,gem5/gem5,Weil0ng/gem5,rallylee/gem5,samueldotj/TeeRISC-Simulator,markoshorro/gem5,aclifton/cpeg853-gem5,zlfben/gem5,SanchayanMaity/gem5,rjschof/gem5,sobercoder/gem5,qizenguf/MLC-STT,samueldotj/TeeRISC-Simulator,briancoutinho0905/2dsampling,SanchayanMaity/gem5,TUD-OS/gem5-dtu,yb-kim/gemV,powerjg/gem5-ci-test,austinharris/gem5-riscv,kaiyuanl/gem5,gedare/gem5,briancoutinho0905/2dsampling