isdn: capi: make capi_class constant

Since commit 43a7206b ("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 capi_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 <gregkh@linuxfoundation.org>
Signed-off-by: Ricardo B. Marliere <ricardo@marliere.net>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240305-class_cleanup-isdn-v1-2-6f0edca75b61@marliere.netSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/isdn/capi/capi.c

@@ -49,7 +49,9 @@ MODULE_LICENSE("GPL");
 /* -------- driver information -------------------------------------- */
 
 static DEFINE_MUTEX(capi_mutex);
-static struct class *capi_class;
+static const struct class capi_class = {
+	.name = "capi",
+};
 static int capi_major = 68;		/* allocated */
 
 module_param_named(major, capi_major, uint, 0);
@@ -1393,18 +1395,19 @@ static int __init capi_init(void)
 		kcapi_exit();
 		return major_ret;
 	}
-	capi_class = class_create("capi");
-	if (IS_ERR(capi_class)) {
+
+	ret = class_register(&capi_class);
+	if (ret) {
 		unregister_chrdev(capi_major, "capi20");
 		kcapi_exit();
-		return PTR_ERR(capi_class);
+		return ret;
 	}
 
-	device_create(capi_class, NULL, MKDEV(capi_major, 0), NULL, "capi20");
+	device_create(&capi_class, NULL, MKDEV(capi_major, 0), NULL, "capi20");
 
 	if (capinc_tty_init() < 0) {
-		device_destroy(capi_class, MKDEV(capi_major, 0));
-		class_destroy(capi_class);
+		device_destroy(&capi_class, MKDEV(capi_major, 0));
+		class_unregister(&capi_class);
 		unregister_chrdev(capi_major, "capi20");
 		kcapi_exit();
 		return -ENOMEM;
@@ -1427,8 +1430,8 @@ static void __exit capi_exit(void)
 {
 	proc_exit();
 
-	device_destroy(capi_class, MKDEV(capi_major, 0));
-	class_destroy(capi_class);
+	device_destroy(&capi_class, MKDEV(capi_major, 0));
+	class_unregister(&capi_class);
 	unregister_chrdev(capi_major, "capi20");
 
 	capinc_tty_exit();