backlight: ktd2801: Make timing struct static

backlight: ktd2801: Make timing struct static

The struct containing the KTD2801 timing can be made static as it's not
referenced outside the KTD2801 driver. Do this to prevent sparse
complaints.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202402100625.M0RkJhMh-lkp@intel.com/
Signed-off-by: Duje Mihanović <duje.mihanovic@skole.hr>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20240210-ktd2801-static-v1-1-90ad2e2e8483@skole.hr
Signed-off-by: Lee Jones <lee@kernel.org>