Staging: iio: adis16220: fix up my fixup for some sysfs attribute permissions

They should be writable by root, not readable.
Doh, stupid me with the wrong flags.

Reported-by: Jonathan Cameron <jic23@cam.ac.uk>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Cc: Barry Song <Barry.Song@analog.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>