s2io: fix warning in drivers/net/s2io.c

this warning:

  drivers/net/s2io.c: In function ‘rx_intr_handler’:
  drivers/net/s2io.c:7369: warning: ‘lro’ may be used uninitialized in this function

triggers because GCC does not recognize the (correct) error flow
between:

 - s2io_club_tcp_session()and 'lro'

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

drivers/net/s2io.c

@@ -7367,7 +7367,7 @@ static int rx_osm_handler(struct ring_info *ring_data, struct RxD_t * rxdp)
 	int ring_no = ring_data->ring_no;
 	u16 l3_csum, l4_csum;
 	unsigned long long err = rxdp->Control_1 & RXD_T_CODE;
-	struct lro *lro;
+	struct lro *uninitialized_var(lro);
 	u8 err_mask;
 
 	skb->dev = dev;