pm80xx: Fix for Incorrect DMA Unmapping of SG List

In pm8001_ccb_task_free(), the dma unmapping is done based on
ccb->n_elem value. This should be initialized to zero in the
task_abort(). Otherwise, pm8001_ccb_task_free() will try for
dma_unmap_sg() which is invalid for task abort and can lead to
kernel crash.

Changes From V1:
None

Signed-off-by: Viswas G <Viswas.G@pmcs.com>

Reviewed-by: Suresh Thiagarajan <Suresh.Thiagarajan@pmcs.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Jack Wang <jinpu.wang@profitbricks.com>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: James Bottomley <JBottomley@Odin.com>