leds: turris-omnia: check for LED_COLOR_ID_RGB instead LED_COLOR_ID_MULTI

LED core does not allow LED_COLOR_ID_MULTI for now and instead for RGB
LEDs prefers LED_COLOR_ID_RGB.

Signed-off-by: Marek Behún <kabel@kernel.org>
Fixes: 77dce3a2 ("leds: disallow /sys/class/leds/*:multi:* for now")
Signed-off-by: Pavel Machek <pavel@ucw.cz>