Fix clippy errors

kernel/src/arch/x86_64/processing/threading/mod.rs

@@ -16,13 +16,13 @@ pub struct Thread {
 pub struct ThreadId(u64);
 
 impl ThreadId {
-    pub fn as_u64(&self) -> u64 {
+    pub const fn as_u64(&self) -> u64 {
         self.0
     }
 
     fn new() -> Self {
         use core::sync::atomic::{AtomicU64, Ordering};
         static NEXT_THREAD_ID: AtomicU64 = AtomicU64::new(1);
-        ThreadId(NEXT_THREAD_ID.fetch_add(1, Ordering::Relaxed))
+        Self(NEXT_THREAD_ID.fetch_add(1, Ordering::Relaxed))
     }
 }