Input: serio_driver - drop private pointer

Nobody uses it anymore.
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

include/linux/serio.h

@@ -54,7 +54,6 @@ struct serio {
 #define to_serio_port(d)	container_of(d, struct serio, dev)
 
 struct serio_driver {
-	void *private;
 	const char *description;
 
 	const struct serio_device_id *id_table;