ASoC: meson: t9015: mark OF related data as maybe unused

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

  sound/soc/meson/t9015.c:315:34: warning: ‘t9015_ids’ defined but not used [-Wunused-const-variable=]
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20201125164452.89239-9-krzk@kernel.orgSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/meson/t9015.c

@@ -312,7 +312,7 @@ static int t9015_probe(struct platform_device *pdev)
 					       &t9015_dai, 1);
 }
 
-static const struct of_device_id t9015_ids[] = {
+static const struct of_device_id t9015_ids[] __maybe_unused = {
 	{ .compatible = "amlogic,t9015", },
 	{ }
 };