video: fbdev: pxafb: add missing of_node_put() in of_get_pxafb_mode_info()

This node pointer is returned by of_graph_get_next_endpoint() with
refcount incremented in this function. of_node_put() on it before
exitting this function.

Found by Coccinelle.

Signed-off-by: Wei Yongjun <weiyj.lk@gmail.com>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>