ah6: fix error return code

Return a negative error code on failure.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@@
identifier ret; expression e1,e2;
@@
(
if (\(ret < 0\|ret != 0\))
 { ... return ret; }
|
ret = 0
)
... when != ret = e1
    when != &ret
*if(...)
{
  ... when != ret = e2
      when forall
 return ret;
}
// </smpl>
Signed-off-by: NJulia Lawall <Julia.Lawall@lip6.fr>
Acked-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/ah6.c

@@ -577,8 +577,10 @@ static int ah6_input(struct xfrm_state *x, struct sk_buff *skb)
 
 	work_iph = ah_alloc_tmp(ahash, nfrags + sglists, hdr_len +
 				ahp->icv_trunc_len + seqhi_len);
-	if (!work_iph)
+	if (!work_iph) {
+		err = -ENOMEM;
 		goto out;
+	}
 
 	auth_data = ah_tmp_auth((u8 *)work_iph, hdr_len);
 	seqhi = (__be32 *)(auth_data + ahp->icv_trunc_len);