leds: cht-wcove: Mark cht_wc_leds_brightness_get() static

cht_wc_leds_brightness_get() is only used internally, mark it static.

Cc: Yauhen Kharuzhy <jekhor@gmail.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202305260008.QCRrKILf-lkp@intel.com/


Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230525183317.129232-1-hdegoede@redhat.com