fix: lookup new vnode may cause freeing parent vnode

Close #I3MYP4

Change-Id: I03b19a74ae5340aa6c7cdc84d044c469873c1648

fs/vfs/fs_open.c

@@ -225,14 +225,17 @@ int fp_open(char *fullpath, int oflags, mode_t mode)
 
   if ((ret != OK) && (oflags & O_CREAT) && vnode)
     {
+      vnode->useCount++;
       /* if file not exist, but parent dir of the file is exist */
       if (VfsVnodePermissionCheck(vnode, (WRITE_OP | EXEC_OP)))
         {
           ret = -EACCES;
+          vnode->useCount--;
           VnodeDrop();
           goto errout_without_count;
         }
       ret = do_creat(&vnode, fullpath, mode);
+      vnode->useCount--;
       if (ret != OK)
         {
           VnodeDrop();

fs/vfs/fs_rename.c

@@ -196,7 +196,9 @@ int do_rename(int oldfd, const char *oldpath, int newfd, const char *newpath)
       ret = -ENOSYS;
       goto errout_with_vnode;
     }
+  new_parent_vnode->useCount++;
   ret = old_vnode->vop->Rename(old_vnode, new_parent_vnode, oldname, newname);
+  new_parent_vnode->useCount--;
   if (ret < 0)
     {
       goto errout_with_vnode;