Add ATA_QCFLAG_EH_SCHEDULED.  If this flag is set, the qc is owned by
EH and normal completion path is not allowed to finish it.  This patch
doesn't actually use this flag.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>