scsi: aic7xxx: aic79xx: fix potential null pointer dereference on ahd

If AHD_DEBUG is enabled and ahd_platform_alloc fails then ahd is set to
null and the debug printk dereferences ahd when passing it to ahd_name.
Fix this by moving the debug printk to before the call to
ahd_platform_alloc where ahd is not null at that point.

Detected by CoverityScan, CID#100296 ("Explicit null dereference")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>