leds/led-class: Add missing put_device()

Devices found by class_find_device must be freed with put_device().
Otherwise the reference count will not work properly.

Fixes: a96aa64c ("leds/led-class: Handle LEDs with the same name")
Reported-by: Alan Tull <delicious.quinoa@gmail.com>
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>