target: do not require a transport_complete for SCF_TRANSPORT_TASK_SENSE

tcmu needs to pass raw sense to target_complete_cmd, but a a
transport_complete callout is akward to implement for it.

This moves the check for SCF_TRANSPORT_TASK_SENSE so any backend
can pass sense.

Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>