of_graph_get_next_endpoint() returns device_node with refcnt increased,
but these is no of_node_put() for it.

The patch adds one on error and normal paths.

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Reviewed-by: Nicholas Mc Guire <der.herr@hofr.at>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>