leds: turris-omnia: Inform about missing LED gamma correction feature in the MCU driver

If the LED gamma correction feature is missing in the MCU firmware,
inform about this in the MCU firmware probe function instead of LED
driver probe function, so that all the feature checks are in one place.

Signed-off-by: Marek Behún <kabel@kernel.org>
Link: https://lore.kernel.org/r/20241111100355.6978-10-kabel@kernel.org


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