leds: leds-menf21bmc.c: Use devm_led_class_register

Use resource-managed function devm_led_classdev_register instead
of led_classdev_register, consequently remove redundant
menf21bmc_led_remove function.
Also drop the unneeded label err_free_leds.

Signed-off-by: Muhammad Falak R Wani <falakreyaz@gmail.com>
Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>