xen: remove DEFINE_XENBUS_DRIVER() macro

The DEFINE_XENBUS_DRIVER() macro looks a bit weird and causes sparse
errors.

Replace the uses with standard structure definitions instead.  This is
similar to pci and usb device registration.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>

drivers/xen/xen-pciback/xenbus.c

@@ -719,11 +719,13 @@ static const struct xenbus_device_id xen_pcibk_ids[] = {
 	{""},
 };
 
-static DEFINE_XENBUS_DRIVER(xen_pcibk, DRV_NAME,
+static struct xenbus_driver xen_pcibk_driver = {
+	.name                   = DRV_NAME,
+	.ids                    = xen_pcibk_ids,
 	.probe			= xen_pcibk_xenbus_probe,
 	.remove			= xen_pcibk_xenbus_remove,
 	.otherend_changed	= xen_pcibk_frontend_changed,
-);
+};
 
 const struct xen_pcibk_backend *__read_mostly xen_pcibk_backend;