cnic: ensure ulp_type is not negative

`ulp_type' is signed, make sure it is not negative
when we read the array element.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Acked-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>