ASoC: codecs: src4xxx-i2c: Mark OF related data as maybe unused

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

  sound/soc/codecs/src4xxx-i2c.c:27:34: error: ‘src4xxx_of_match’ defined but not used [-Werror=unused-const-variable=]
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230310214333.274903-9-krzysztof.kozlowski@linaro.orgSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/src4xxx-i2c.c

@@ -24,7 +24,7 @@ static const struct i2c_device_id src4xxx_i2c_ids[] = {
 };
 MODULE_DEVICE_TABLE(i2c, src4xxx_i2c_ids);
 
-static const struct of_device_id src4xxx_of_match[] = {
+static const struct of_device_id src4xxx_of_match[] __maybe_unused = {
 	{ .compatible = "ti,src4392", },
 	{ }
 };