We assume that "pd" can be null on the previous line, and throughout the
function so we should check it here as well. This was introduced by 9b2c2ff7a1c0 "mv643xx_eth: use sw csum for big packets"
Signed-off-by: Dan Carpenter <error27@gmail.com> Acked-by: Lennert Buytenhek <buytenh@wantstofly.org> Signed-off-by: David S. Miller <davem@davemloft.net>