Staging: iio: fix up the iio_get_new_idr_val comment

improve the comment a bit

Cc: Greg KH <greg@kroah.com>
Cc: Jonathan Cameron <jic23@cam.ac.uk>
Cc: Sonic Zhang <sonic.adi@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>