hwmon: (ina3221) mark PM functions as __maybe_unused

When CONFIG_PM_SLEEP is disabled, we get a warning about unused
suspend/resume functions:

drivers/hwmon/ina3221.c:451:12: error: 'ina3221_resume' defined but not used [-Werror=unused-function]
 static int ina3221_resume(struct device *dev)
drivers/hwmon/ina3221.c:428:12: error: 'ina3221_suspend' defined but not used [-Werror=unused-function]
 static int ina3221_suspend(struct device *dev)

Picking the correct #ifdef check is hard, so let's remove
that check and instead mark the functions as __maybe_unused
to let the compiler silently drop them instead.

Fixes: 7de1ab9dac8e ("hwmon: (ina3221) Add suspend and resume functions")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>