USB: backlight, appledisplay: fix incomplete registration failure handling

On error while registering backlight, return it to caller instead of
returning 0.
Mark struct backlight_ops as const.
Signed-off-by: NBruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/usb/misc/appledisplay.c

@@ -179,7 +179,7 @@ static int appledisplay_bl_get_brightness(struct backlight_device *bd)
 		return pdata->msgdata[1];
 }
 
-static struct backlight_ops appledisplay_bl_data = {
+static const struct backlight_ops appledisplay_bl_data = {
 	.get_brightness	= appledisplay_bl_get_brightness,
 	.update_status	= appledisplay_bl_update_status,
 };
@@ -283,6 +283,7 @@ static int appledisplay_probe(struct usb_interface *iface,
 						&appledisplay_bl_data);
 	if (IS_ERR(pdata->bd)) {
 		dev_err(&iface->dev, "Backlight registration failed\n");
+		retval = PTR_ERR(pdata->bd);
 		goto error;
 	}