leds: pca955x: use devm_led_classdev_register

This lets us remove the loop doing the cleanup in case of failure and
also the remove handler of the i2c_driver.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>