libata: Populate host-to-device FIS "auxiliary" field

SATA 3.1 added an "auxiliary" field to the host-to-device FIS.
Populate the host-to-device FIS with the new field via the
taskfile struct.

Signed-off-by: Marc Carino <marc.ceeeee@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>