timers: Mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where fall through is indeed expected.

Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Cc: Frederic Weisbecker <[e-mail]>
Cc: John Stultz <[e-mail]>
Cc: Stephen Boyd <[e-mail]>
Link: https://lkml.kernel.org/r/20190123081413.GA3949@embeddedor

kernel/time/hrtimer.c

···
 	switch (state) {
 	case ODEBUG_STATE_ACTIVE:
 		WARN_ON(1);
-
+		/* fall through */
 	default:
 		return false;
 	}

kernel/time/tick-broadcast.c

···
 	switch (mode) {
 	case TICK_BROADCAST_FORCE:
 		tick_broadcast_forced = 1;
+		/* fall through */
 	case TICK_BROADCAST_ON:
 		cpumask_set_cpu(cpu, tick_broadcast_on);
 		if (!cpumask_test_and_set_cpu(cpu, tick_broadcast_mask)) {

kernel/time/timer.c

···
 
 	case ODEBUG_STATE_ACTIVE:
 		WARN_ON(1);
-
+		/* fall through */
 	default:
 		return false;
 	}