ASoC: da7218: 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/da7218.c:2281:34: warning: ‘da7218_of_match’ defined but not used [-Wunused-const-variable=]
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20201125164452.89239-18-krzk@kernel.orgSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/da7218.c

@@ -2278,12 +2278,14 @@ static irqreturn_t da7218_irq_thread(int irq, void *data)
  * DT
  */
 
+#ifdef CONFIG_OF
 static const struct of_device_id da7218_of_match[] = {
 	{ .compatible = "dlg,da7217", .data = (void *) DA7217_DEV_ID },
 	{ .compatible = "dlg,da7218", .data = (void *) DA7218_DEV_ID },
 	{ }
 };
 MODULE_DEVICE_TABLE(of, da7218_of_match);
+#endif
 
 static inline int da7218_of_get_id(struct device *dev)
 {