SysFSTools: allow longer pci domains

SysFSTools: allow longer pci domains

by default, there is only one pci domain ('0000'), but there are systems
where there are more, and they don't need to be exactly 4 characters
long (see [0]), so extend that regex to allow domains 4 characters or
longer

0: https://forum.proxmox.com/threads/problem-with-gpu-passthrough-in-a-virtual-machine.105720/

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>