hwmon: (ina2xx) Fix build warning

The following build warning is seen if CONFIG_OF is disabled.

drivers/hwmon/ina2xx.c:510:34: warning:
	‘ina2xx_of_match’ defined but not used

Mark ina2xx_of_match as __maybe_unused to fix the problem.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/ina2xx.c

@@ -507,7 +507,7 @@ static const struct i2c_device_id ina2xx_id[] = {
 };
 MODULE_DEVICE_TABLE(i2c, ina2xx_id);
 
-static const struct of_device_id ina2xx_of_match[] = {
+static const struct of_device_id __maybe_unused ina2xx_of_match[] = {
 	{
 		.compatible = "ti,ina219",
 		.data = (void *)ina219