rtc: ds1672: quiet maybe-unused variable warning

When CONFIG_OF is disabled then the matching table is not referenced.
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210202112219.3610853-7-alexandre.belloni@bootlin.com

drivers/rtc/rtc-ds1672.c

@@ -139,7 +139,7 @@ static const struct i2c_device_id ds1672_id[] = {
 };
 MODULE_DEVICE_TABLE(i2c, ds1672_id);
 
-static const struct of_device_id ds1672_of_match[] = {
+static const __maybe_unused struct of_device_id ds1672_of_match[] = {
 	{ .compatible = "dallas,ds1672" },
 	{ }
 };