Re: [v3 13/13] docs: iio: add documentation for BNO055 driver

[Andrea Merello]

[...]

> > +IIO attributes for unavailable measurements (e.g. Euler angles when fusion
> > +mode is disabled) just read zero.
>
> Hmm. Should probably return -EBUSY as 0 could be a valid value.
>

While it seems reasonable,  that can be easily done while reading from
sysfs, but how do we handle this when reading from buffer?
Right now both sysfs and buffer read zero from unused chans, which it
is at least consistent..