libata depended on SCSI command to have the correct length when
tranlating it into an ATA command.  This generally worked for commands
issued by SCSI HLD but user could issue arbitrary broken command using
sg interface.

Also, when building ATAPI command, full command size was always
copied.  Because some ATAPI devices needs bytes after CDB cleared, if
upper layer doesn't clear bytes after CDB, such devices will
malfunction.  This necessiated recent clear-garbage-after-CDB fix in
sg interfaces.  However, scsi_execute() isn't fixed yet and HL-DT-ST
DVD-RAM GSA-H30N malfunctions on initialization commands issued from
SCSI.

This patch makes xlat functions always consider SCSI cmd_len.  Each
translation function checks for proper cmd_len and ATAPI translaation
clears bytes after CDB.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Douglas Gilbert <dougg@torque.net>
Signed-off-by: Jeff Garzik <jeff@garzik.org>