leds: tlc591xx: use devm_led_classdev_register_ext()

Use devm_led_classdev_register_ext() to pass the fwnode to the LED core.
The fwnode can then be used by the firmware core to create meaningful
names.

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