net: wwan: hwsim: make wwan_hwsim_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 wwan_hwsim_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]>
Acked-by: Sergey Ryazanov <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/wwan/wwan_hwsim.c

···
 module_param_named(devices, wwan_hwsim_devsnum, int, 0444);
 MODULE_PARM_DESC(devices, "Number of simulated devices");
 
-static struct class *wwan_hwsim_class;
+static const struct class wwan_hwsim_class = {
+	.name = "wwan_hwsim",
+};
 
 static struct dentry *wwan_hwsim_debugfs_topdir;
 static struct dentry *wwan_hwsim_debugfs_devcreate;
···
 	spin_unlock(&wwan_hwsim_devs_lock);
 
 	dev->dev.release = wwan_hwsim_dev_release;
-	dev->dev.class = wwan_hwsim_class;
+	dev->dev.class = &wwan_hwsim_class;
 	dev_set_name(&dev->dev, "hwsim%u", dev->id);
 
 	spin_lock_init(&dev->ports_lock);
···
 	if (!wwan_wq)
 		return -ENOMEM;
 
-	wwan_hwsim_class = class_create("wwan_hwsim");
-	if (IS_ERR(wwan_hwsim_class)) {
-		err = PTR_ERR(wwan_hwsim_class);
+	err = class_register(&wwan_hwsim_class);
+	if (err)
 		goto err_wq_destroy;
-	}
 
 	wwan_hwsim_debugfs_topdir = debugfs_create_dir("wwan_hwsim", NULL);
 	wwan_hwsim_debugfs_devcreate =
···
 	wwan_hwsim_free_devs();
 	flush_workqueue(wwan_wq);	/* Wait deletion works completion */
 	debugfs_remove(wwan_hwsim_debugfs_topdir);
-	class_destroy(wwan_hwsim_class);
+	class_unregister(&wwan_hwsim_class);
 err_wq_destroy:
 	destroy_workqueue(wwan_wq);
 
···
 	wwan_hwsim_free_devs();
 	flush_workqueue(wwan_wq);	/* Wait deletion works completion */
 	debugfs_remove(wwan_hwsim_debugfs_topdir);
-	class_destroy(wwan_hwsim_class);
+	class_unregister(&wwan_hwsim_class);
 	destroy_workqueue(wwan_wq);
 }