!116 pipe函数节点操作错误后退出分支，未对g_pipecreated全局变量回退，导致下一次pipe调用存在问题

Merge pull request !116 from zhangfanfan2/master

drivers/pipes/pipe.c

@@ -354,6 +354,9 @@ errout_with_wrfd:
 
 errout_with_driver:
   unregister_driver(devname);
+  (void)sem_wait(&g_pipesem);
+  g_pipecreated &= ~(1 << pipeno);
+  (void)sem_post(&g_pipesem);
 
 errout_with_dev:
   if (dev)