scsi: mac_scsi: Fix MAC_SCSI=m option when SCSI=m

The mac_scsi driver still gets disabled when SCSI=m. This should have
been fixed back when I enabled the tristate but I didn't see the bug.

Fixes: 6e9ae6d5 ("[PATCH] mac_scsi: Add module option to Kconfig")
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>