fbcon: convert last two unregister_con_driver call to do_unregister_con_driver

There are only two place use unregister_con_driver now, this patch
convert them to do_unregister_con_driver too, then we can delete
unregister_con_driver whos function can be achieved with do_unregister_con_driver
easily to reduce code size and duplication.

Signed-off-by: Wang YanQing <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/vt/vt.c

···
  */
 void give_up_console(const struct consw *csw)
 {
-	unregister_con_driver(csw);
+	console_lock();
+	do_unregister_con_driver(csw);
+	console_unlock();
 }
 
 static int __init vtconsole_class_init(void)

drivers/video/console/fbcon.c

···
 	fbcon_deinit_device();
 	device_destroy(fb_class, MKDEV(0, 0));
 	fbcon_exit();
+	do_unregister_con_driver(&fb_con);
 	console_unlock();
-	unregister_con_driver(&fb_con);
 }	
 
 module_exit(fb_console_exit);