intel_cstates: ignore negative time-delta values

I have no idea why this can happen or if there is a deeper problem.

Should fix #16546.

Change-Id: Ia160e293eabefae636ce4c861864c99b0aaa68db
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3717
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>

src/add-ons/kernel/power/cpuidle/intel_cstates/intel_cstates.cpp

@@ -100,7 +100,9 @@ cstates_idle(void)
 	bigtime_t delta = system_time() - start;
 	locker.Unlock();
 
-	sIdleTime[cpu] = (idleTime + delta) / 2;
+	// Negative delta shouldn't happen, but apparently it does...
+	if (delta >= 0)
+		sIdleTime[cpu] = (idleTime + delta) / 2;
 }