[TIPC] Fix for NULL pointer dereference

This fixes a bug spotted by the coverity checker, bug id #366. If
(mod(seqno - prev) != 1) we set buf to NULL, dereference it in the for
case, and set it to whatever value happes to be at adress 0+next, if it
happens to be non-zero, we even stay in the loop. It seems that the author
intended to break there.
Signed-off-by: NEric Sesterhenn <snakebyte@gmx.de>
Signed-off-by: NPer Liden <per.liden@ericsson.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/tipc/bcast.c

@@ -349,8 +349,10 @@ static void tipc_bclink_peek_nack(u32 dest, u32 sender_tag, u32 gap_after, u32 g
 		for (; buf; buf = buf->next) {
 			u32 seqno = buf_seqno(buf);
 
-			if (mod(seqno - prev) != 1)
+			if (mod(seqno - prev) != 1) {
 				buf = NULL;
+				break;
+			}
 			if (seqno == gap_after)
 				break;
 			prev = seqno;