hwmon: (pmbus/ir38064) Mark ir38064_of_match as __maybe_unused

If CONFIG_PM is not enabled, the following warning is reported.

drivers/hwmon/pmbus/ir38064.c:54:34: warning:
	unused variable 'ir38064_of_match'

Mark it as __maybe_unused.

Reported-by: kernel test robot <lkp@intel.com>
Cc: Arthur Heymans <arthur.heymans@9elements.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>