libata: fix EH-related lockup by properly cleaning EH command list

Yet another hack due to the fact that libata is the only user of SCSI's
->eh_strategy_handler() hook.

drivers/scsi/libata-scsi.c

@@ -385,6 +385,7 @@ int ata_scsi_error(struct Scsi_Host *host)
 	 * appropriate place
 	 */
 	host->host_failed--;
+	INIT_LIST_HEAD(&host->eh_cmd_q);
 
 	DPRINTK("EXIT\n");
 	return 0;