ASoC: pcm1789: 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/pcm1789-i2c.c:36:34: warning: ‘pcm1789_of_match’ defined but not used [-Wunused-const-variable=]
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20201125164452.89239-28-krzk@kernel.orgSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/pcm1789-i2c.c

@@ -33,11 +33,13 @@ static int pcm1789_i2c_remove(struct i2c_client *client)
 	return pcm1789_common_exit(&client->dev);
 }
 
+#ifdef CONFIG_OF
 static const struct of_device_id pcm1789_of_match[] = {
 	{ .compatible = "ti,pcm1789", },
 	{ }
 };
 MODULE_DEVICE_TABLE(of, pcm1789_of_match);
+#endif
 
 static const struct i2c_device_id pcm1789_i2c_ids[] = {
 	{ "pcm1789", 0 },