[libata] Prevent warning during PMP error recovery

Cleanup sff_pio_task_link when a command is cancel while the
pio_task thread has been scheduled.

Signed-off-by: Gwendal Grignou <gwendal@google.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
diff --git a/drivers/ata/libata-sff.c b/drivers/ata/libata-sff.c
index 996a7a5..c24127d 100644
--- a/drivers/ata/libata-sff.c
+++ b/drivers/ata/libata-sff.c
@@ -1333,6 +1333,7 @@
 
 	cancel_delayed_work_sync(&ap->sff_pio_task);
 	ap->hsm_task_state = HSM_ST_IDLE;
+	ap->sff_pio_task_link = NULL;
 
 	if (ata_msg_ctl(ap))
 		ata_port_dbg(ap, "%s: EXIT\n", __func__);