cpuidle: menu: Fix menu_select() for CPUIDLE_DRIVER_STATE_START == 0

Commit a9ceb78b (cpuidle,menu: use interactivity_req to disable
polling) exposed a bug in menu_select() causing it to return -1
on systems with CPUIDLE_DRIVER_STATE_START equal to zero, although
it should have returned 0.  As a result, idle states are not entered
by CPUs on those systems.

Namely, on the systems in question data->last_state_idx is initially
equal to -1 and the above commit modified the condition that would
have caused it to be changed to 0 to be less likely to trigger which
exposed the problem.  However, setting data->last_state_idx initially
to -1 doesn't make sense at all and on the affected systems it should
always be set to CPUIDLE_DRIVER_STATE_START (ie. 0) unconditionally,
so make that happen.

Fixes: a9ceb78b (cpuidle,menu: use interactivity_req to disable polling)
Reported-and-tested-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpuidle/governors/menu.c

@@ -294,8 +294,6 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 		data->needs_update = 0;
 	}
 
-	data->last_state_idx = CPUIDLE_DRIVER_STATE_START - 1;
-
 	/* Special case when user has set very strict latency requirement */
 	if (unlikely(latency_req == 0))
 		return 0;
@@ -326,6 +324,8 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 	if (latency_req > interactivity_req)
 		latency_req = interactivity_req;
 
+	if (CPUIDLE_DRIVER_STATE_START > 0) {
+		data->last_state_idx = CPUIDLE_DRIVER_STATE_START - 1;
 		/*
 		 * We want to default to C1 (hlt), not to busy polling
 		 * unless the timer is happening really really soon.
@@ -334,6 +334,9 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 		    !drv->states[CPUIDLE_DRIVER_STATE_START].disabled &&
 			dev->states_usage[CPUIDLE_DRIVER_STATE_START].disable == 0)
 			data->last_state_idx = CPUIDLE_DRIVER_STATE_START;
+	} else {
+		data->last_state_idx = CPUIDLE_DRIVER_STATE_START;
+	}
 
 	/*
 	 * Find the idle state with the lowest power while satisfying