leds: leds-mc13783: Use of_get_child_by_name() instead of refcount hack

of_find_node_by_name() calls of_node_put() on its "from" parameter.
To counter this, mc13xxx_led_probe_dt() calls of_node_get() first.

Use of_get_child_by_name() instead to get rid of the refcount hack.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: linux-leds@vger.kernel.org
Signed-off-by: Bryan Wu <cooloney@gmail.com>