ASoC: codecs: zl38060: Mark OF related data as maybe unused

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

  sound/soc/codecs/zl38060.c:611:34: error: ‘zl38_dt_ids’ defined but not used [-Werror=unused-const-variable=]
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230310214333.274903-10-krzysztof.kozlowski@linaro.orgSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/zl38060.c

@@ -608,7 +608,7 @@ static int zl38_spi_probe(struct spi_device *spi)
 					       &zl38_dai, 1);
 }
 
-static const struct of_device_id zl38_dt_ids[] = {
+static const struct of_device_id zl38_dt_ids[] __maybe_unused = {
 	{ .compatible = "mscc,zl38060", },
 	{ /* sentinel */ }
 };