[media] v4l: omap3isp: Fix OF node double put when parsing OF graph

When parsing the graph the driver loops over all endpoints using
of_graph_get_next_endpoint(). The function handles reference counting of
the passed and returned nodes, so the returned node's reference count
must not be decreased manually in the normal path.

Move the offending of_node_put() call to the error path that requires
manual reference count handling.

Reported-by: H. Nikolaus Schaller <hns@goldelico.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>