scsi: hisi_sas: Free slot later in slot_complete_vx_hw()

If an SSP/SMP IO times out, it may be actually in reality be
simultaneously processing completion of the slot in
slot_complete_vx_hw().

Then if the slot is freed in slot_complete_vx_hw() (this IPTT is freed
and it may be re-used by other slot), and we may abort the wrong slot in
hisi_sas_abort_task().

So to solve the issue, free the slot after the check of
SAS_TASK_STATE_ABORTED in slot_complete_vx_hw().

Signed-off-by: Xiang Chen <chenxiang66@hisilicon.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>