iio: humidity: hts221: Move symbol exports into IIO_HTS221 namespace

iio: humidity: hts221: Move symbol exports into IIO_HTS221 namespace

Avoid unnecessary pollution of the global symbol namespace by
moving library functions in to a specific namespace and import
that into the drivers that make use of the functions.

For more info: https://lwn.net/Articles/760045/

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/20220220181522.541718-7-jic23@kernel.org
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/20220604161223.461847-4-jic23@kernel.org