[SCSI] aacraid: Fix default FIB size

Received from Mark Salyzyn.

If the adapter has not instructed us otherwise that it can handle a
'large' FIB, then it can handle at most a 2KB FIB.

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