pci_add_capability returns a strictly positive value on success, correct asserts. Cc: dmitry@daynix.com Cc: jasowang@redhat.com Cc: kraxel@redhat.com Cc: alex.williamson@redhat.com Cc: armbru@redhat.com Cc: marcel@redhat.com Signed-off-by: Mao Zhongyi <maozy.fnst@cn.fujitsu.com> Reviewed-by: Marcel Apfelbaum <marcel@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>