drivers/atm/atmtcp.c: fix error return code

Convert a zero return value on error to a negative one, as returned
elsewhere in the function.

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: Julia Lawall <[e-mail]>
Acked-by: Chas Williams <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/atm/atmtcp.c

···
 	out_vcc = find_vcc(dev, ntohs(hdr->vpi), ntohs(hdr->vci));
 	read_unlock(&vcc_sklist_lock);
 	if (!out_vcc) {
+		result = -EUNATCH;
 		atomic_inc(&vcc->stats->tx_err);
 		goto done;
 	}