vfs: stat_recursive should return -ENOSYS if stat callback is NULL

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
Change-Id: Ic342b6fff112d24c7355ddc8aa0937dfc544f1b4

fs/vfs/fs_stat.c

@@ -120,6 +120,10 @@ static int stat_recursive(FAR const char *path,
 
           ret = inode->u.i_mops->stat(inode, desc.relpath, buf);
         }
+      else
+        {
+          ret = -ENOSYS;
+        }
     }
   else
 #endif