hwmon: (ltc4151) Fix build warning

If CONFIG_OF is not enabled, the following build warning is observed.

drivers/hwmon/ltc4151.c:211:34: warning:
	‘ltc4151_match’ defined but not used

Mark ltc4151_match as __maybe_unused to fix the problem.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/ltc4151.c

@@ -208,7 +208,7 @@ static const struct i2c_device_id ltc4151_id[] = {
 };
 MODULE_DEVICE_TABLE(i2c, ltc4151_id);
 
-static const struct of_device_id ltc4151_match[] = {
+static const struct of_device_id __maybe_unused ltc4151_match[] = {
 	{ .compatible = "lltc,ltc4151" },
 	{},
 };