SCSI: add missing cdb clearing in scsi_execute()

Clear-garbage-after-CDB patch missed scsi_execute() and it causes some
ODDs (HL-DT-ST DVD-RAM GSA-H30N) choke during SCSI scan.  Note that
this patch is only for -stable.  There is another more reliable fix
for this problem proposed for devel tree.

http://thread.gmane.org/gmane.linux.ide/14605/focus=14605



Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Douglas Gilbert <dougg@torque.net>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>