cnic: Fix Context ID space calculation

Include FCoE CID space only for E2_PLUS devices.  Remove old CID
offset adjustments that are no longer needed.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Reviewed-by: Bhanu Prakash Gollapudi <bprakash@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>