hwmon: (max6639) Convert to dev_pm_ops

The I2C specific PM operations have been deprecated and printing a
warning on boot for over a year now.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
[guenter.roeck@ericsson.com: Added missing #ifdef around pm functions]
Cc: stable@vger.kernel.org # 3.0+
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>