[media] v4l: flash led class: Fix of_node release in probe() error path

The sub-device's OF node was used (of_node_get()) if it was set, but
device's OF node was always put. Fix this.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>