staging:iio: Rip out helper for software rings.

It seemed like a good idea at the time, it wasn't.
The code with this in place is larger and more complex for
no real gain.  Basically we've cleaned up the core around
it so much that this no longer makes sense.

Only really effects the lis3l02dq driver.

Signed-off-by: Jonathan Cameron <jic23@cam.acuk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>