iio: chemical: scd30: Move symbol exports into IIO_SCD30 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: Tomasz Duszynski <tomasz.duszynski@octakon.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>