api: fix cargo clippy errors

Cargo clippy wants to let us add `Default` implementation for PseudoFs,
just do it.

error: you should consider adding a `Default` implementation for `PseudoFs`
  --> src/api/pseudo_fs.rs:80:5
   |
80 | /     pub fn new() -> Self {
81 | |         let root_inode = Arc::new(PseudoInode::new(ROOT_ID, ROOT_ID, String::from("/")));
82 | |         let fs = PseudoFs {
83 | |             next_inode: AtomicU64::new(PSEUDOFS_NEXT_INODE),
...  |
94 | |         fs
95 | |     }
   | |_____^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#new_without_default
   = note: `-D clippy::new-without-default` implied by `-D warnings`

Signed-off-by: Zizheng Bian <[email protected]>

Author: ZizhengBian

src/api/pseudo_fs.rs

@@ -329,6 +329,12 @@ impl PseudoFs {
     }
 }
 
+impl Default for PseudoFs {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl FileSystem for PseudoFs {
     type Inode = Inode;
     type Handle = Handle;