scsi: mac53c94: Fix warning comparing pointer to 0

Fix the following coccicheck warning:

drivers/scsi/mac53c94.c:237:12-13: WARNING comparing pointer to 0

Link: https://lore.kernel.org/r/1647244711-31575-1-git-send-email-baihaowen@meizu.com


Signed-off-by: Haowen Bai <baihaowen@meizu.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>