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>
diff --git a/drivers/pci/xen-pcifront.c b/drivers/pci/xen-pcifront.c
index 53df39a..116ca37 100644
--- a/drivers/pci/xen-pcifront.c
+++ b/drivers/pci/xen-pcifront.c
@@ -1136,11 +1136,13 @@
 	{""},
 };
 
-static DEFINE_XENBUS_DRIVER(xenpci, "pcifront",
+static struct xenbus_driver xenpci_driver = {
+	.name			= "pcifront",
+	.ids			= xenpci_ids,
 	.probe			= pcifront_xenbus_probe,
 	.remove			= pcifront_xenbus_remove,
 	.otherend_changed	= pcifront_backend_changed,
-);
+};
 
 static int __init pcifront_init(void)
 {