[RXRPC] net/rxrpc/ar-connection.c: fix NULL dereference

This patch fixes a NULL dereference spotted by the Coverity checker.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/rxrpc/ar-connection.c b/net/rxrpc/ar-connection.c
index 43cb3e0..482750e 100644
--- a/net/rxrpc/ar-connection.c
+++ b/net/rxrpc/ar-connection.c
@@ -211,7 +211,7 @@
 		conn->header_size = sizeof(struct rxrpc_header);
 	}
 
-	_leave(" = %p{%d}", conn, conn->debug_id);
+	_leave(" = %p{%d}", conn, conn ? conn->debug_id : 0);
 	return conn;
 }