hinic: skb_pad() frees on error

The skb_pad() function frees the skb on error, so this code has a double
free.

Fixes: 00e57a6d ("net-next/hinic: Add Tx operation")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>