orangefs: Remove useless xattr prefix arguments

Mike,

On Fri, Jun 3, 2016 at 9:44 PM, Mike Marshall <hubcap@omnibond.com> wrote:
> We use the return value in this one line you changed, our userspace code gets
> ill when we send it (-ENOMEM +1) as a key length...

ah, my mistake.  Here's a fixed version.

Thanks,
Andreas

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Mike Marshall <hubcap@omnibond.com>