smmu: Clear SMMUPciBus pointer cache when system reset

smmu: Clear SMMUPciBus pointer cache when system reset

s->smmu_pcibus_by_bus_num is a SMMUPciBus pointer cache indexed
by bus number, bus number may not always be a fixed value,
i.e., guest reboot to different kernel which set bus number with
different algorithm.

This could lead to smmu_iommu_mr() providing the wrong iommu MR.

Suggested-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Message-Id: <20240125073706.339369-3-zhenzhong.duan@intel.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>