s2io: fix uninitialized compile warning

drivers/net/s2io.c:7559: warning: ‘tcp_len’ may be used uninitialized in this function
Signed-off-by: NShan Wei <shanwei@cn.fujitsu.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/s2io.c

@@ -7556,7 +7556,7 @@ static int rx_osm_handler(struct ring_info *ring_data, struct RxD_t * rxdp)
 			 */
 			skb->ip_summed = CHECKSUM_UNNECESSARY;
 			if (ring_data->lro) {
-				u32 tcp_len;
+				u32 tcp_len = 0;
 				u8 *tcp;
 				int ret = 0;