leds: multicolor: Use led_get_color_name() function

led_get_color_name() is a safer alternative to led_colors.

led-class-multicolor.c is the only external user of led_colors and its
removal allows unexporting the array.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20240613-cros_ec-led-v3-2-500b50f41e0f@weissschuh.net


Signed-off-by: Lee Jones <lee@kernel.org>