[SCSI] aha152x: stop poking at saved scsi_cmnd members

Stop poking into the old_ & co scsi_cmnd fields that should only be used
in the EH code.  Untested, but this is required to move ahead with the
EH fixes.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>