bnx2x: Use correct FW constant for header padding

the value of the constant is the same, but it's clearer to use original
constant provided by HSI

Signed-off-by: Dmitry Kravkov <dmitry@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>