ASoC: tas571x: mark OF related data as maybe unused

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

  sound/soc/codecs/tas571x.c:892:34: warning: ‘tas571x_of_match’ defined but not used [-Wunused-const-variable=]
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20201125164452.89239-7-krzk@kernel.orgSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/tas571x.c

@@ -773,7 +773,7 @@ static struct snd_soc_dai_driver tas571x_dai = {
 	.ops = &tas571x_dai_ops,
 };
 
-static const struct of_device_id tas571x_of_match[];
+static const struct of_device_id tas571x_of_match[] __maybe_unused;
 
 static int tas571x_i2c_probe(struct i2c_client *client,
 			     const struct i2c_device_id *id)
@@ -889,7 +889,7 @@ static int tas571x_i2c_remove(struct i2c_client *client)
 	return 0;
 }
 
-static const struct of_device_id tas571x_of_match[] = {
+static const struct of_device_id tas571x_of_match[] __maybe_unused = {
 	{ .compatible = "ti,tas5707", .data = &tas5707_chip, },
 	{ .compatible = "ti,tas5711", .data = &tas5711_chip, },
 	{ .compatible = "ti,tas5717", .data = &tas5717_chip, },