device_create returns &struct device pointer on success, or ERR_PTR() on error.
Thus if led_classdev_register fails, led_cdev->dev is always not NULL.

If IS_ERR(eeepc->tpd_led.dev) is ture, it means led_classdev_register fails.
If (asus->tpd_led.dev) is NULL, it means we call eeepc_led_exit before
calling led_classdev_register for &eeepc->tpd_led.

We only want to call led_classdev_unregister for sucessfully registered
led_classdev, then we should check (!IS_ERR_OR_NULL(eeepc->tpd_led.dev)).
Signed-off-by: NAxel Lin <axel.lin@gmail.com>
Acked-by: NCorentin Chary <corentin.chary@gmail.com>
Signed-off-by: NMatthew Garrett <mjg@redhat.com>