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 <[e-mail]>
Closes: https://lore.kernel.org/oe-kbuild-all/[e-mail]/
Signed-off-by: Duje Mihanović <[e-mail]>
Reviewed-by: Daniel Thompson <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/video/backlight/ktd2801-backlight.c

···
 #define KTD2801_MAX_BRIGHTNESS		255
 
 /* These values have been extracted from Samsung's driver. */
-const struct expresswire_timing ktd2801_timing = {
+static const struct expresswire_timing ktd2801_timing = {
 	.poweroff_us = 2600,
 	.detect_delay_us = 150,
 	.detect_us = 270,