iio: pressure: bmp280: Use unsigned data types for raw sensor data

iio: pressure: bmp280: Use unsigned data types for raw sensor data

The raw sensor data that have not been compensated yet cannot be
signed values, so use unsigned ones. Also, compensated pressure
values cannot be negative so use unsigned also there.

Also, drop redundant cast of data->t_fine variable from s32 to s32.

Signed-off-by: Vasileios Amoiridis <vassilisamir@gmail.com>
Link: https://lore.kernel.org/r/20240508165207.145554-5-vassilisamir@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>