thermal: step_wise: Revert optimization

Commit 178c2490 ("thermal: step_wise:
cdev only needs update on a new target state") broke driver acerhdf.
That driver abused the step_wise thermal governor until the bang_bang
governor was available, and the optimization broke this usage model.

Kernels v3.12 to v3.18 are affected. In v3.19 the acerhdf driver was
switched to the bang_bang governor and that solved the problem.

For kernels v3.12 to v3.17, the bang_bang governor isn't available
yet so the easiest fix is to revert the optimization.
Signed-off-by: Jean Delvare <jdelvare@suse.de>
Reported-by: Dieter Jurzitza (https://bugzilla.opensuse.org/show_bug.cgi?id=925961)
Tested-by: Peter Feuerer <peter@piie.net>
Tested-by: Dieter Jurzitza

drivers/thermal/step_wise.c

@@ -140,9 +140,6 @@ static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
 		old_target = instance->target;
 		instance->target = get_target_state(instance, trend, throttle);
 
-		if (old_target == instance->target)
-			continue;
-
 		/* Activate a passive thermal instance */
 		if (old_target == THERMAL_NO_TARGET &&
 			instance->target != THERMAL_NO_TARGET)