Bus: Only update port cache when there is an item to update it with.
Bus: Only update port cache when there is an item to update it with.

--HG--
extra : convert_revision : 84848fd48bb9e6693a0518c862364142b1969aa8

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