staging:iio: unwind the IIO_IN -> IIO_VOLTAGE define

This was originally there to avoid churn during a complex change.
Now everything is stable lets get rid of this as it is missleading
and confusing.

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
25 files changed