Fix pci_vga_init() not to ignore bus argument

Commit a414c306 converted all VGA devices to qdev.  It used
pci_create_simple() for all devices, except for this one it used
pci_create().  That's wrong, because it uses PCI bus#0 regardless of
the bus argument.  Fix by switching to pci_create_noinit().

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>