i2c: synquacer: mark OF related data as maybe unused

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

  drivers/i2c/busses/i2c-synquacer.c:632:34: error: ‘synquacer_i2c_dt_ids’ defined but not used [-Werror=unused-const-variable=]
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

drivers/i2c/busses/i2c-synquacer.c

@@ -629,7 +629,7 @@ static int synquacer_i2c_remove(struct platform_device *pdev)
 	return 0;
 };
 
-static const struct of_device_id synquacer_i2c_dt_ids[] = {
+static const struct of_device_id synquacer_i2c_dt_ids[] __maybe_unused = {
 	{ .compatible = "socionext,synquacer-i2c" },
 	{ /* sentinel */ }
 };