leds: turris-omnia: Use sysfs_emit() instead of sprintf()

Use the dedicated sysfs_emit() function instead of sprintf() in sysfs
attribute accessor brightness_show().

Signed-off-by: Marek Behún <kabel@kernel.org>
Link: https://lore.kernel.org/r/20230802160748.11208-4-kabel@kernel.org


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