leds: ns2: Add of_node_put() before return

Each iteration of for_each_child_of_node puts the previous node, but in
the case of a return from the middle of the loop, there is no put, thus
causing a memory leak. Hence create a new label, err_node_put, that puts
the previous node before returning the required value. Edit the mid-loop
return sites to instead go to this new label.
Issue found with Coccinelle.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>