scsi: megaraid: silence a static checker bug

If we had more than 32 megaraid cards then it would cause memory
corruption.  That's not likely, of course, but it's handy to enforce it
and make the static checker happy.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>