gpu-compute: fix uninitialized member bug in GPUDynInst
gpu-compute: fix uninitialized member bug in GPUDynInst

the n_reg field in the GPUDynInst is not currently set in the constructor.
if it is not set externally, there are assertion failures that may occur
if the random value it gets is just right. here we set it to 0 by default.

KuroeKurose/gem5,TUD-OS/gem5-dtu,briancoutinho0905/2dsampling,gem5/gem5,SanchayanMaity/gem5,HwisooSo/gemV-update,sobercoder/gem5,rallylee/gem5,powerjg/gem5-ci-test,cancro7/gem5,cancro7/gem5,aclifton/cpeg853-gem5,gem5/gem5,HwisooSo/gemV-update,Weil0ng/gem5,powerjg/gem5-ci-test,gem5/gem5,HwisooSo/gemV-update,gedare/gem5,powerjg/gem5-ci-test,gedare/gem5,Weil0ng/gem5,SanchayanMaity/gem5,qizenguf/MLC-STT,qizenguf/MLC-STT,Weil0ng/gem5,aclifton/cpeg853-gem5,SanchayanMaity/gem5,gedare/gem5,gedare/gem5,aclifton/cpeg853-gem5,KuroeKurose/gem5,rallylee/gem5,SanchayanMaity/gem5,cancro7/gem5,TUD-OS/gem5-dtu,rjschof/gem5,gem5/gem5,gem5/gem5,cancro7/gem5,powerjg/gem5-ci-test,powerjg/gem5-ci-test,rjschof/gem5,aclifton/cpeg853-gem5,cancro7/gem5,rallylee/gem5,Weil0ng/gem5,sobercoder/gem5,qizenguf/MLC-STT,gem5/gem5,SanchayanMaity/gem5,briancoutinho0905/2dsampling,sobercoder/gem5,KuroeKurose/gem5,qizenguf/MLC-STT,briancoutinho0905/2dsampling,qizenguf/MLC-STT,rallylee/gem5,cancro7/gem5,rallylee/gem5,TUD-OS/gem5-dtu,qizenguf/MLC-STT,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,KuroeKurose/gem5,gedare/gem5,Weil0ng/gem5,HwisooSo/gemV-update,TUD-OS/gem5-dtu,rjschof/gem5,powerjg/gem5-ci-test,TUD-OS/gem5-dtu,rallylee/gem5,briancoutinho0905/2dsampling,gedare/gem5,HwisooSo/gemV-update,SanchayanMaity/gem5,rjschof/gem5,rjschof/gem5,gedare/gem5,sobercoder/gem5,powerjg/gem5-ci-test,qizenguf/MLC-STT,Weil0ng/gem5,sobercoder/gem5,HwisooSo/gemV-update,briancoutinho0905/2dsampling,aclifton/cpeg853-gem5,aclifton/cpeg853-gem5,KuroeKurose/gem5,gem5/gem5,rjschof/gem5,cancro7/gem5,Weil0ng/gem5,KuroeKurose/gem5,HwisooSo/gemV-update,rallylee/gem5,sobercoder/gem5,rjschof/gem5,sobercoder/gem5,aclifton/cpeg853-gem5,SanchayanMaity/gem5,briancoutinho0905/2dsampling,KuroeKurose/gem5,briancoutinho0905/2dsampling