misc: phantom: make phantom_class constant

Now that the driver core allows for struct class to be in read-only
memory, we should make all 'class' structures declared at build time
placing them into read-only memory, instead of having to be dynamically
allocated at runtime.

Cc: Arnd Bergmann <[e-mail]>
Reviewed-by: Jiri Slaby <[e-mail]>
Link: https://lore.kernel.org/r/2023102434-font-feast-98e3@gregkh
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/misc/phantom.c

···
 #define PHB_NOT_OH		2
 
 static DEFINE_MUTEX(phantom_mutex);
-static struct class *phantom_class;
 static int phantom_major;
+
+static const struct class phantom_class = {
+	.name = "phantom",
+};
 
 struct phantom_device {
 	unsigned int opened;
···
 		goto err_irq;
 	}
 
-	if (IS_ERR(device_create(phantom_class, &pdev->dev,
+	if (IS_ERR(device_create(&phantom_class, &pdev->dev,
 				 MKDEV(phantom_major, minor), NULL,
 				 "phantom%u", minor)))
 		dev_err(&pdev->dev, "can't create device\n");
···
 	struct phantom_device *pht = pci_get_drvdata(pdev);
 	unsigned int minor = MINOR(pht->cdev.dev);
 
-	device_destroy(phantom_class, MKDEV(phantom_major, minor));
+	device_destroy(&phantom_class, MKDEV(phantom_major, minor));
 
 	cdev_del(&pht->cdev);
 
···
 	int retval;
 	dev_t dev;
 
-	phantom_class = class_create("phantom");
-	if (IS_ERR(phantom_class)) {
-		retval = PTR_ERR(phantom_class);
+	retval = class_register(&phantom_class);
+	if (retval) {
 		printk(KERN_ERR "phantom: can't register phantom class\n");
 		goto err;
 	}
-	retval = class_create_file(phantom_class, &class_attr_version.attr);
+	retval = class_create_file(&phantom_class, &class_attr_version.attr);
 	if (retval) {
 		printk(KERN_ERR "phantom: can't create sysfs version file\n");
 		goto err_class;
···
 err_unchr:
 	unregister_chrdev_region(dev, PHANTOM_MAX_MINORS);
 err_attr:
-	class_remove_file(phantom_class, &class_attr_version.attr);
+	class_remove_file(&phantom_class, &class_attr_version.attr);
 err_class:
-	class_destroy(phantom_class);
+	class_unregister(&phantom_class);
 err:
 	return retval;
 }
···
 
 	unregister_chrdev_region(MKDEV(phantom_major, 0), PHANTOM_MAX_MINORS);
 
-	class_remove_file(phantom_class, &class_attr_version.attr);
-	class_destroy(phantom_class);
+	class_remove_file(&phantom_class, &class_attr_version.attr);
+	class_unregister(&phantom_class);
 
 	pr_debug("phantom: module successfully removed\n");
 }