fix clippy lints

examples/donate.c

@@ -53,6 +53,7 @@ static void spinner(void)
     rt_task_sleep(10);
     for (;;)
     {
+        rt_task_yield();
     }
 }
 

rust/examples/donate.rs

@@ -44,7 +44,9 @@ fn spinner() {
     rt::task::drop_privilege();
     sequence(1);
     rt::task::sleep(10);
-    loop {}
+    loop {
+        rt::task::yield_now();
+    }
 }
 
 fn donator() {

rust/src/sync/mutex.rs

@@ -152,7 +152,7 @@ mod tests {
     fn try_lock() {
         test_init();
         mutex!(MUTEX, i32, 0);
-        MUTEX.try_lock().map(|mut x| *x += 1);
+        if let Some(mut x) = MUTEX.try_lock() { *x += 1; }
         assert!(*MUTEX.lock() == 1);
     }
 }