xen-blkfront: module exit handling adjustments

The blkdev major must be released upon exit, or else the module can't
attach to devices using the same majors upon being loaded again. Also
avoid leaking the minor tracking bitmap.
Signed-off-by: NJan Beulich <jbeulich@suse.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/block/xen-blkfront.c

@@ -1500,7 +1500,9 @@ module_init(xlblk_init);
 
 static void __exit xlblk_exit(void)
 {
-	return xenbus_unregister_driver(&blkfront_driver);
+	xenbus_unregister_driver(&blkfront_driver);
+	unregister_blkdev(XENVBD_MAJOR, DEV_NAME);
+	kfree(minors);
 }
 module_exit(xlblk_exit);