staging: lustre: obdclass: remove pointless struct lustre_mount_data2

This is used to pass a void* and NULL to lustre_fill_super().
It is easier just to pass the void*.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>