dyndbg: make ddebug_tables list LIFO for add/remove_module

loadable modules are the last in on this list, and are the only
modules that could be removed.  ddebug_remove_module() searches from
head, but ddebug_add_module() uses list_add_tail().  Change it to
list_add() for a micro-optimization.

Acked-by: <jbaron@akamai.com>
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Link: https://lore.kernel.org/r/20200719231058.1586423-11-jim.cromie@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

lib/dynamic_debug.c

@@ -895,7 +895,7 @@ int ddebug_add_module(struct _ddebug *tab, unsigned int n,
 	dt->ddebugs = tab;
 
 	mutex_lock(&ddebug_lock);
-	list_add_tail(&dt->link, &ddebug_tables);
+	list_add(&dt->link, &ddebug_tables);
 	mutex_unlock(&ddebug_lock);
 
 	v2pr_info("%u debug prints in module %s\n", n, dt->mod_name);