leds: tlc591xx: Mark OF related data as maybe unused

The driver can be compile tested with !CONFIG_OF making certain data
unused:

  drivers/leds/leds-tlc591xx.c:138:34: error: ‘of_tlc591xx_leds_match’ defined but not used [-Werror=unused-const-variable=]
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230311111717.252019-1-krzysztof.kozlowski@linaro.org

drivers/leds/leds-tlc591xx.c

@@ -135,7 +135,7 @@ static const struct regmap_config tlc591xx_regmap = {
 	.max_register = 0x1e,
 };
 
-static const struct of_device_id of_tlc591xx_leds_match[] = {
+static const struct of_device_id of_tlc591xx_leds_match[] __maybe_unused = {
 	{ .compatible = "ti,tlc59116",
 	  .data = &tlc59116 },
 	{ .compatible = "ti,tlc59108",