DDF: use LBA_OFFSET macro instead of lba_offset field

DDF: use LBA_OFFSET macro instead of lba_offset field

Remove the lba_offset field from struct vcl. This field acted as
a "cache" for the address of the lba_offset field in the vd_config
structure. This isn't useful any more if there are multiple
vd_configs in a vcl.

This patch also adds __cpu_to_be64 in two places where it has been
quite obviously forgotten (ddf_set_disk, ddf_activate_spare).

Signed-off-by: Martin Wilck <mwilck@arcor.de>
Signed-off-by: NeilBrown <neilb@suse.de>