atari_scsi: Fix SCSI host ID setting

The NVRAM location of this byte is 16, as documented in
http://toshyp.atari.org/en/004009.html



This was confirmed by Michael Schmitz, by setting the SCSI host ID
under EmuTOS and then checking the value in /proc/driver/nvram and
/dev/nvram under Linux.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Tested-by: Michael Schmitz <schmitzmic@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>