leds: sc27xx-blt: Use generic support for composing LED names

Switch to using generic LED support for composing LED class
device name.

Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Reviewed-by: Baolin Wang <baolin.wang@linaro.org>
Acked-by: Pavel Machek <pavel@ucw.cz>