We already have a generic PCI_BUILD_BDF() macro in "hw/pci/pci.h"
to pack these values, use it.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20201012124506.3406909-3-philmd@redhat.com>