Now that libata has slave_link, there's no need to keep ugly merged
SCR access.  Drop it and use slave_link instead.  This results in
simpler code and much better separate link handling for master and
slave.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJeff Garzik <jgarzik@redhat.com>