iio: pressure: dps310: introduce consistent error handling

Align error handling with `dps310_calculate_temp`, where it's not
possible to differentiate between errors and valid calculations by
checking if the returned value is negative.

Signed-off-by: Thomas Haemmerle <thomas.haemmerle@leica-geosystems.com>
Link: https://lore.kernel.org/r/20240415105030.1161770-3-thomas.haemmerle@leica-geosystems.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>