scsi: mac53c94: Fix warning comparing pointer to 0

Fix the following coccicheck warning:

./drivers/scsi/mac53c94.c:470:29-30: WARNING comparing pointer to 0.
./drivers/scsi/mac53c94.c:349:12-13: WARNING comparing pointer to 0.

Link: https://lore.kernel.org/r/1615349771-81106-1-git-send-email-jiapeng.chong@linux.alibaba.com


Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>