iio: pressure: bmp280: Simplify bmp280 calibration data reading

On bmp280 and bme280, the temperature and pressure calibration parameters
are available on a contiguous memory region. Considering this arrangement,
simplified the calibration reading function by using only one buffer
to read in batch temperature and pressure registers.

Signed-off-by: Angel Iglesias <ang.iglesiasg@gmail.com>
Link: https://lore.kernel.org/r/96d81282c95006d857f4d836d2ff3ee0740a85a0.1663025017.git.ang.iglesiasg@gmail.com


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