[PATCH] libata: make ata_qc_issue complete failed qcs

There is no reason for the issuer to diddle with a failed qc as the
issuer has complete control over when a qc gets freed (usually in
->complete_fn).  Make ata_qc_issue() responsible for completing qcs
which failed to issue.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>