thermal: rcar-thermal: update thermal zone only when temperature changes

Avoid updating the thermal zone in case an IRQ was triggered but the
temperature didn't effectively change.
Note this is not a driver issue.
Below is a captured debug trace illustrating the purpose of this patch:
out of 8 thermal zone updates, only 2 are actually necessary.

[ 41.120000] rcar_thermal_work(): cctemp=25000
[ 41.120000] rcar_thermal_work(): nctemp=30000
[ 41.120000] rcar_thermal_work(): temp is now 30000C, update thermal zone
[ 58.990000] rcar_thermal_work(): cctemp=30000
[ 58.990000] rcar_thermal_work(): nctemp=30000
[ 58.990000] rcar_thermal_work(): same temp, do not update thermal zone
[ 59.290000] rcar_thermal_work(): cctemp=30000
[ 59.290000] rcar_thermal_work(): nctemp=30000
[ 59.290000] rcar_thermal_work(): same temp, do not update thermal zone
[ 59.590000] rcar_thermal_work(): cctemp=30000
[ 59.590000] rcar_thermal_work(): nctemp=30000
[ 59.590000] rcar_thermal_work(): same temp, do not update thermal zone
[ 59.890000] rcar_thermal_work(): cctemp=30000
[ 59.890000] rcar_thermal_work(): nctemp=30000
[ 59.890000] rcar_thermal_work(): same temp, do not update thermal zone
[ 60.190000] rcar_thermal_work(): cctemp=30000
[ 60.190000] rcar_thermal_work(): nctemp=30000
[ 60.190000] rcar_thermal_work(): same temp, do not update thermal zone
[ 60.490000] rcar_thermal_work(): cctemp=30000
[ 60.490000] rcar_thermal_work(): nctemp=30000
[ 60.490000] rcar_thermal_work(): same temp, do not update thermal zone
[ 60.790000] rcar_thermal_work(): cctemp=30000
[ 60.790000] rcar_thermal_work(): nctemp=35000
[ 60.790000] rcar_thermal_work(): temp is now 35000C, update thermal zone

I suspect this may be due to sensor sampling accuracy / fluctuation,
but no formal proof.

Signed-off-by: Patrick Titiano <[e-mail]>
Acked-by: Kuninori Morimoto <[e-mail]>
Signed-off-by: Zhang Rui <[e-mail]>

drivers/thermal/rcar_thermal.c

···
 static void rcar_thermal_work(struct work_struct *work)
 {
 	struct rcar_thermal_priv *priv;
+	unsigned long cctemp, nctemp;
 
 	priv = container_of(work, struct rcar_thermal_priv, work.work);
 
+	rcar_thermal_get_temp(priv->zone, &cctemp);
 	rcar_thermal_update_temp(priv);
 	rcar_thermal_irq_enable(priv);
-	thermal_zone_device_update(priv->zone);
+
+	rcar_thermal_get_temp(priv->zone, &nctemp);
+	if (nctemp != cctemp)
+		thermal_zone_device_update(priv->zone);
 }
 
 static u32 rcar_thermal_had_changed(struct rcar_thermal_priv *priv, u32 status)