leds: various: use dev_of_node(dev) instead of dev->of_node

The dev_of_node function should be preferred.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Cc: Orson Zhai <orsonzhai@gmail.com>
Cc: Baolin Wang <baolin.wang7@gmail.com>
Cc: Chunyan Zhang <zhang.lyra@gmail.com>
Cc: Sean Wang <sean.wang@mediatek.com>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Cc: Riku Voipio <riku.voipio@iki.fi>
Signed-off-by: Pavel Machek <pavel@ucw.cz>