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>