net: ppp: make ppp_class constant

Since commit 43a7206b0963 ("driver core: class: make class_register() take
a const *"), the driver core allows for struct class to be in read-only
memory, so move the ppp_class structure to be declared at build time
placing it into read-only memory, instead of having to be dynamically
allocated at boot time.

Suggested-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Ricardo B. Marliere <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/ppp/ppp_generic.c

···
 
 static const struct net_device_ops ppp_netdev_ops;
 
-static struct class *ppp_class;
+static const struct class ppp_class = {
+	.name = "ppp",
+};
 
 /* per net-namespace data */
 static inline struct ppp_net *ppp_pernet(struct net *net)
···
 		goto out_net;
 	}
 
-	ppp_class = class_create("ppp");
-	if (IS_ERR(ppp_class)) {
-		err = PTR_ERR(ppp_class);
+	err = class_register(&ppp_class);
+	if (err)
 		goto out_chrdev;
-	}
 
 	err = rtnl_link_register(&ppp_link_ops);
 	if (err) {
···
 	}
 
 	/* not a big deal if we fail here :-) */
-	device_create(ppp_class, NULL, MKDEV(PPP_MAJOR, 0), NULL, "ppp");
+	device_create(&ppp_class, NULL, MKDEV(PPP_MAJOR, 0), NULL, "ppp");
 
 	return 0;
 
 out_class:
-	class_destroy(ppp_class);
+	class_unregister(&ppp_class);
 out_chrdev:
 	unregister_chrdev(PPP_MAJOR, "ppp");
 out_net:
···
 		pr_err("PPP: removing module but units remain!\n");
 	rtnl_link_unregister(&ppp_link_ops);
 	unregister_chrdev(PPP_MAJOR, "ppp");
-	device_destroy(ppp_class, MKDEV(PPP_MAJOR, 0));
-	class_destroy(ppp_class);
+	device_destroy(&ppp_class, MKDEV(PPP_MAJOR, 0));
+	class_unregister(&ppp_class);
 	unregister_pernet_device(&ppp_net_ops);
 }