via-velocity: remove null pointer check on array tdinfo->skb_dma

tdinfo->skb_dma is a 7 element array of dma_addr_t hence cannot be
null, so the pull pointer check on tdinfo->skb_dma  is redundant.
Remove it.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: David S. Miller <davem@davemloft.net>