s2io: fix uninitialized compile warning

drivers/net/s2io.c:7559: warning: ‘tcp_len’ may be used uninitialized in this function

Signed-off-by: Shan Wei <shanwei@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/s2io.c b/drivers/net/s2io.c
index 39c17ce..2ad6364 100644
--- a/drivers/net/s2io.c
+++ b/drivers/net/s2io.c
@@ -7556,7 +7556,7 @@
 			 */
 			skb->ip_summed = CHECKSUM_UNNECESSARY;
 			if (ring_data->lro) {
-				u32 tcp_len;
+				u32 tcp_len = 0;
 				u8 *tcp;
 				int ret = 0;