ASoC: rt5660: skip of_device_id table when !CONFIG_OF

The driver can match by multiple methods.  Its of_device_id table is
referenced via of_match_ptr() so it will be unused for !CONFIG_OF
builds:

  sound/soc/codecs/rt5660.c:1238:34: warning: ‘rt5660_of_match’ defined but not used [-Wunused-const-variable=]
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20201125164452.89239-30-krzk@kernel.orgSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/rt5660.c

@@ -1235,11 +1235,13 @@ static const struct i2c_device_id rt5660_i2c_id[] = {
 };
 MODULE_DEVICE_TABLE(i2c, rt5660_i2c_id);
 
+#ifdef CONFIG_OF
 static const struct of_device_id rt5660_of_match[] = {
 	{ .compatible = "realtek,rt5660", },
 	{},
 };
 MODULE_DEVICE_TABLE(of, rt5660_of_match);
+#endif
 
 #ifdef CONFIG_ACPI
 static const struct acpi_device_id rt5660_acpi_match[] = {