viostor: Initialize system_io_bus_number in VirtIoFindAdapter
viostor: Initialize system_io_bus_number in VirtIoFindAdapter

system_io_bus_number is left uninitialized which makes the driver
fail to load in VMs with non-trivial bus configuration, for example
Q35 / PCIe.

vrozenfe/kvm-guest-drivers-windows,daynix/kvm-guest-drivers-windows,YanVugenfirer/kvm-guest-drivers-windows,gnif/kvm-guest-drivers-windows,YanVugenfirer/virtio-win-arm,daynix/kvm-guest-drivers-windows,ladipro/kvm-guest-drivers-windows,YanVugenfirer/virtio-win-arm,virtio-win/kvm-guest-drivers-windows,vrozenfe/kvm-guest-drivers-windows,gnif/kvm-guest-drivers-windows,vrozenfe/kvm-guest-drivers-windows,YanVugenfirer/kvm-guest-drivers-windows,virtio-win/kvm-guest-drivers-windows,gnif/kvm-guest-drivers-windows,vrozenfe/kvm-guest-drivers-windows,daynix/kvm-guest-drivers-windows,YanVugenfirer/kvm-guest-drivers-windows,virtio-win/kvm-guest-drivers-windows,daynix/kvm-guest-drivers-windows,ladipro/kvm-guest-drivers-windows,virtio-win/kvm-guest-drivers-windows,YanVugenfirer/kvm-guest-drivers-windows,YanVugenfirer/virtio-win-arm,vrozenfe/kvm-guest-drivers-windows,daynix/kvm-guest-drivers-windows,YanVugenfirer/kvm-guest-drivers-windows,virtio-win/kvm-guest-drivers-windows,YanVugenfirer/virtio-win-arm,gnif/kvm-guest-drivers-windows,ladipro/kvm-guest-drivers-windows,ladipro/kvm-guest-drivers-windows