target/ppc: Fix kvmppc_load_htab_chunk() error reporting

If kvmppc_load_htab_chunk() fails, its return value is propagated up
to vmstate_load(). It should thus be a negative errno, not -1 (which
maps to EPERM and would lure the user into thinking that the problem
is necessarily related to a lack of privilege).

Return the error reported by KVM or ENOSPC in case of short write.
While here, propagate the error message through an @errp argument
and have the caller to print it with error_report_err() instead
of relying on fprintf().

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <160371604713.305923.5264900354159029580.stgit@bahia.lan>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>