[SCSI] aacraid: bad BUG_ON fix

This was noticed by Doug Bazamic and the fix found by Mark Salyzyn at
Adaptec.

There was an error in the BUG_ON() statement that validated the
calculated fib size which can cause the driver to panic.

Signed-off-by: Mark Haverkamp <markh@osdl.org>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>