isci: isci_request_cleanup_completed_loiterer checks task before task_done

In the condition where outstanding I/Os are being cleaned from the device
requests in process list, the cleanup function needs to check that the
request is actually a sas-task and not a task management function.

Signed-off-by: Jeff Skirvin <jeffrey.d.skirvin@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>