tests: Don't set PCI address in usb-controller-default tests

tests: Don't set PCI address in usb-controller-default tests

We want to ensure that libvirt will automatically allocate the
PCI address, and setting it ourselves ahead of time will
prevent that from happening.

In the case of q35, this change will cause additional PCI
controllers to show up. That's desirable, as it demonstrates
the behavior libvirt users will actually see.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>