leds: tlc591xx: fix leak of device node iterator

In one of the error paths of the for_each_child_of_node loop in
tlc591xx_probe, add missing call to of_node_put.

Fixes: 1ab4531a ("leds: tlc591xx: simplify driver by using the managed led API")

Signed-off-by: Tobias Jordan <kernel@cdqe.de>
Reviewed-by: Marek Behún <kabel@kernel.org>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>