cosa: 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>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/wan/cosa.c

@@ -579,6 +579,7 @@ static int cosa_probe(int base, int irq, int dma)
 		/* Register the network interface */
 		if (!(chan->netdev = alloc_hdlcdev(chan))) {
 			pr_warn("%s: alloc_hdlcdev failed\n", chan->name);
+			err = -ENOMEM;
 			goto err_hdlcdev;
 		}
 		dev_to_hdlc(chan->netdev)->attach = cosa_net_attach;