staging:iio:resolver:ad2s120x cleanup.

I've currently squashed the vel + pos combined attribute.  If people need them
precisely paired I doubt they will get them from the sysfs interface anyway.
If that is a requirement it should come via a buffer implementation.

Note this patch leaves the completely non standard interface alone.
That will get fixed later.

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>