net: Fix off-by-one in skb_dma_map

The unwind loop iterates down to -1 instead of stopping at 0 and ends up
accessing ->frags[-1].

Signed-off-by: Dimitris Michailidis <dm@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
1 file changed