Merge pull request #15113 from kaspar030/fix_ztimer_spin

ztimer: fix ztimer_spin() time_left == duration case

sys/include/ztimer.h

@@ -456,7 +456,10 @@ void ztimer_sleep(ztimer_clock_t *clock, uint32_t duration);
  */
 static inline void ztimer_spin(ztimer_clock_t *clock, uint32_t duration) {
     uint32_t end = ztimer_now(clock) + duration;
-    while ((end - ztimer_now(clock)) < duration) {}
+
+    /* Rely on integer overflow. `end - now` will be smaller than `duration`,
+     * counting down, until it underflows to UINT32_MAX. Loop ends then. */
+    while ((end - ztimer_now(clock)) <= duration) {}
 }
 
 /**