[media] xilinx-vipp: remove unnecessary of_node_put

of_graph_get_next_endpoint(node, ep) decrements refcount on
ep. When next==NULL we break and refcount on ep is decremented
again.

Signed-off-by: Franck Jullien <franck.jullien@odyssee-systemes.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>