kdd: fix build again

kdd: fix build again

Restore Tim's patch. The one that was committed was recreated by me
because git didn't accept my saved copy. I made some mistakes while
recreating that patch and here we are.

Fixes: 3471cafbdda3 ("kdd: stop using [0] arrays to access packet contents")
Reported-by: Michael Young <m.a.young@durham.ac.uk>
Signed-off-by: Wei Liu <wl@xen.org>
Reviewed-by: Tim Deegan <tim@xen.org>
Release-acked-by: Paul Durrant <paul@xen.org>