hsm: fix updateVolumeSize for raw volumes

Change-Id: I08aa24277d11595e82c93b979c2c34fcf9d09c38
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/19279
Reviewed-by: Sergey Gotliv <sgotliv@redhat.com>
Tested-by: Sergey Gotliv <sgotliv@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>