isci: Qualify when the host lock is managed for STP/SATA callbacks.

In the case of internal discovery related STP/SATA I/O started
through sas_execute_task the host lock is not taken by libsas before
calling lldd_execute_task, so the lock should not be managed before
calling back to libsas through task->task_done or sas_task_abort.

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