iio: humidity: hts221: Use EXPORT_SIMPLE_DEV_PM_OPS() to allow compiler to remove dead code.

If CONFIG_PM_SLEEP is not defined using EXPORT_SIMPLE_DEV_PM_OPS()
in conjunction with pm_sleep_ptr() allows the compiler to remove
the unused code and data. This removes the need for __maybe_unused
markings etc.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/20220220181522.541718-6-jic23@kernel.org


Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/20220604161223.461847-3-jic23@kernel.org