leds: ns2: use devres API for getting GPIO descriptors

This drivers leaks GPIO descriptors on driver removal. Use devres API
function devm_gpiod_get_from_of_node instead of gpiod_get_from_of_node
to avoid this.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Cc: Simon Guinot <simon.guinot@sequanux.org>
Cc: Simon Guinot <sguinot@lacie.com>
Cc: Vincent Donnefort <vdonnefort@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Not-for-stable
Signed-off-by: Pavel Machek <pavel@ucw.cz>