leds: tlc591xx: simplify driver by using the managed led API

Use the managed API of the LED class (devm_led_classdev_register()
instead of led_classdev_register()).
This allows us to remove the code used to track-and-destroy the LED devices.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>