hwmon: (tmp103) Fix build warning

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

drivers/hwmon/tmp103.c:173:34: warning:
	‘tmp103_of_match’ defined but not used

Marking tmp103_of_match as __maybe_unused fixes the problem.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>