iio: chemical: scd30: Export dev_pm_ops instead of suspend() and resume()

Whilst here move to the new infrastructure using pm_sleep_ptr()
and EXPORT_DEV_PM_OPS() so as to let the compiler remove the unused
code if CONFIG_SLEEP is not defined.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Tomasz Duszynski <tomasz.duszynski@octakon.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>