ASoC: bd28623: mark OF related data as maybe unused

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

  sound/soc/codecs/bd28623.c:225:34: warning: ‘bd28623_of_match’ defined but not used [-Wunused-const-variable=]
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20201125164452.89239-3-krzk@kernel.orgSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/bd28623.c

@@ -222,7 +222,7 @@ static int bd28623_probe(struct platform_device *pdev)
 					       &soc_dai_bd, 1);
 }
 
-static const struct of_device_id bd28623_of_match[] = {
+static const struct of_device_id bd28623_of_match[] __maybe_unused = {
 	{ .compatible = "rohm,bd28623", },
 	{}
 };