io: update reflink/dedupe ioctl definitions

io: update reflink/dedupe ioctl definitions

The committed version was a pre-review version of the ioctl
interface. Update it to match post-review
version.

[dchinner: I've just aplied the latest patches over the top of
 what I originally committed, so the diff here isn't exactly what
 Darrick originally sent. ]

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>