[PATCH] libata: Fixup ata_sas_queuecmd to handle __ata_scsi_queuecmd failure

Fixes ata_sas_queuecmd to properly handle a failure from
__ata_scsi_queuecmd.

Signed-off-by: Brian King <brking@us.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>