thermal: trip: Simplify computing trip indices

A trip index can be computed right away as a difference between the
value of a trip pointer pointing to the given trip object and the
start of the trips[] table in the given thermal zone, so change
thermal_zone_trip_id() accordingly.

No intentional functional impact (except for some speedup).

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Tested-by: Lukasz Luba <lukasz.luba@arm.com>

Author: rafaeljw

drivers/thermal/thermal_trip.c

@@ -173,12 +173,9 @@ int thermal_zone_set_trip(struct thermal_zone_device *tz, int trip_id,
 int thermal_zone_trip_id(struct thermal_zone_device *tz,
 			 const struct thermal_trip *trip)
 {
-	int i;
-
-	for (i = 0; i < tz->num_trips; i++) {
-		if (&tz->trips[i] == trip)
-			return i;
-	}
-
-	return -ENODATA;
+	/*
+	 * Assume the trip to be located within the bounds of the thermal
+	 * zone's trips[] table.
+	 */
+	return trip - tz->trips;
 }