Fix null pointer dereference in appledisplay driver

Commit 40b20c25 by Len Brown introduced
a null pointer dereference in the appledisplay driver. This patch fixes
it.
Signed-off-by: Michael Hanselmann <linux-kernel@hansmi.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/misc/appledisplay.c

@@ -281,8 +281,8 @@ static int appledisplay_probe(struct usb_interface *iface,
 	/* Register backlight device */
 	snprintf(bl_name, sizeof(bl_name), "appledisplay%d",
 		atomic_inc_return(&count_displays) - 1);
-	pdata->bd = backlight_device_register(bl_name, NULL, NULL,
-						&appledisplay_bl_data);
+	pdata->bd = backlight_device_register(bl_name, NULL,
+		pdata, &appledisplay_bl_data);
 	if (IS_ERR(pdata->bd)) {
 		err("appledisplay: Backlight registration failed");
 		goto error;