[SCSI] aacraid: fib size math fix

Received from Mark Salyzyn from Adaptec.

The size of the command packet's scatter gather list maximum size was
miscalculated in the low range leading to the driver initialization
limiting the maximum i/o size that could go to the Adapter. There were
no negative operational side effects resulting from this bad math, only
a subtle limit in performance of the Adapter at the top end of the
range.

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