leds: triggers: new function led_set_trigger_data()

This is the natural counter part to the already existing
led_get_trigger_data().

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>