Fixed a bug that the efs lock was not be held correctly

easy-fs/src/efs.rs

@@ -112,8 +112,12 @@ impl EasyFileSystem {
 
     pub fn root_inode(efs: &Arc<Mutex<Self>>) -> Inode {
         let block_device = Arc::clone(&efs.lock().block_device);
+        // acquire efs lock temporarily
+        let (block_id, block_offset) = efs.lock().get_disk_inode_pos(0);
+        // release efs lock
         Inode::new(
-            0,
+            block_id,
+            block_offset,
             Arc::clone(efs),
             block_device,
         )