iio: magnetometer: yas530: Correct scaling of magnetic axes

Looks like YAS530 raw values return picotesla and YAS532 nanotesla. Adapt
comments and scaling.

Signed-off-by: Jakob Hauser <jahau@rocketmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/053ab05cb9a0f6b0536ab5e0de57009f513c6f81.1660337264.git.jahau@rocketmail.com


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