examples: use return according to code style

docs/examples/evhiperfifo.c

@@ -424,7 +424,7 @@ static int init_fifo(GlobalInfo *g)
   fprintf(MSG_OUT, "Now, pipe some URL's into > %s\n", fifo);
   ev_io_init(&g->fifo_event, fifo_cb, sockfd, EV_READ);
   ev_io_start(g->loop, &g->fifo_event);
-  return (0);
+  return 0;
 }
 
 int main(int argc, char **argv)

docs/examples/hiperfifo.c

@@ -422,7 +422,7 @@ static int init_fifo(GlobalInfo *g)
   event_assign(&g->fifo_event, g->evbase, sockfd, EV_READ|EV_PERSIST,
                fifo_cb, g);
   event_add(&g->fifo_event, NULL);
-  return (0);
+  return 0;
 }
 
 static void clean_fifo(GlobalInfo *g)