pci_bus.h: tweak include guards

Now that header has been renamed, tweak include guards
to match.
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/pci/pci_bus.h

-#ifndef QEMU_PCI_INTERNALS_H
-#define QEMU_PCI_INTERNALS_H
+#ifndef QEMU_PCI_BUS_H
+#define QEMU_PCI_BUS_H
 
 /*
  * PCI Bus and Bridge datastructures.
@@ -71,4 +71,4 @@ struct PCIBridge {
     const char *bus_name;
 };
 
-#endif /* QEMU_PCI_INTERNALS_H */
+#endif /* QEMU_PCI_BUS_H */