pci: sorting out type confusion in pci_register_bar().

This patch sorts out invalid use of pcibus_t.

In pci_register_bar(), pcibus_t wmask is used.  It should,
however, be uint64_t because it is used to set
pci configuration space value(PCIDevice::wmask)
by pci_set_quad() or pci_set_long().

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
