pci: fix info pci with host bridge.

This patch fixes 525e05147d5a3bdc08caa422d108c1ef71b584b5.
pci host bridge doesn't have header type of bridge.
The check should be by header type, instead of pci class device.

Cc: Blue Swirl <blauwirbel@gmail.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
