ata_scsi_translate allocates from the libata command queue by calling
ata_scsi_qc_new.  If xlat_func returns non-zero, control jumps to
err_out which fails to free the allocated command.  Fix is to add a
new API to free unused commands.
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>