rtc: m41t80: 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/20210202112219.3610853-10-alexandre.belloni@bootlin.com

drivers/rtc/rtc-m41t80.c

@@ -85,7 +85,7 @@ static const struct i2c_device_id m41t80_id[] = {
 };
 MODULE_DEVICE_TABLE(i2c, m41t80_id);
 
-static const struct of_device_id m41t80_of_match[] = {
+static const __maybe_unused struct of_device_id m41t80_of_match[] = {
 	{
 		.compatible = "st,m41t62",
 		.data = (void *)(M41T80_FEATURE_SQ | M41T80_FEATURE_SQ_ALT)