backlight: max8925_bl: Fix error handling path

Properly unregister a previously registered backlight device object in error
handling of max8925_backlight_probe.

Signed-off-by: Axel Lin <[e-mail]>
Signed-off-by: Richard Purdie <[e-mail]>

drivers/video/backlight/max8925_bl.c

···
 	backlight_update_status(bl);
 	return 0;
 out:
+	backlight_device_unregister(bl);
 	kfree(data);
 	return ret;
 }