net: cxgb3_main: Fix a resource leak in a error path in 'init_one()'

A call to 'kfree_skb()' is missing in the error handling path of
'init_one()'.
This is already present in 'remove_one()' but is missing here.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>