cassini: fix warning in drivers/net/cassini.c

this warning:

  drivers/net/cassini.c: In function ‘cas_rx_ringN’:
  drivers/net/cassini.c:2350: warning: ‘skb’ may be used uninitialized in this function

triggers because GCC does not recognize the (correct) error flow
between cas_rx_process_pkt() and 'skb'.

Annotate it.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/cassini.c

@@ -2347,7 +2347,7 @@ static int cas_rx_ringN(struct cas *cp, int ring, int budget)
 	drops = 0;
 	while (1) {
 		struct cas_rx_comp *rxc = rxcs + entry;
-		struct sk_buff *skb;
+		struct sk_buff *uninitialized_var(skb);
 		int type, len;
 		u64 words[4];
 		int i, dring;