drivers/sensor: Make references to driver_api const

Change-Id: I872bf5c748f00bc40e5a1f8992e1e11ad843311c
Signed-off-by: Marcus Shawcroft <marcus.shawcroft@arm.com>
diff --git a/include/sensor.h b/include/sensor.h
index 816d85b..fc7daeb 100644
--- a/include/sensor.h
+++ b/include/sensor.h
@@ -269,9 +269,8 @@
 				  enum sensor_attribute attr,
 				  const struct sensor_value *val)
 {
-	struct sensor_driver_api *api;
+	const struct sensor_driver_api *api = dev->driver_api;
 
-	api = (struct sensor_driver_api *)dev->driver_api;
 	if (!api->attr_set) {
 		return -ENOTSUP;
 	}
@@ -298,9 +297,8 @@
 				     struct sensor_trigger *trig,
 				     sensor_trigger_handler_t handler)
 {
-	struct sensor_driver_api *api;
+	const struct sensor_driver_api *api = dev->driver_api;
 
-	api = (struct sensor_driver_api *)dev->driver_api;
 	if (!api->trigger_set) {
 		return -ENOTSUP;
 	}
@@ -326,9 +324,7 @@
  */
 static inline int sensor_sample_fetch(struct device *dev)
 {
-	struct sensor_driver_api *api;
-
-	api = (struct sensor_driver_api *)dev->driver_api;
+	const struct sensor_driver_api *api = dev->driver_api;
 
 	return api->sample_fetch(dev, SENSOR_CHAN_ALL);
 }
@@ -355,9 +351,7 @@
 static inline int sensor_sample_fetch_chan(struct device *dev,
 					   enum sensor_channel type)
 {
-	struct sensor_driver_api *api;
-
-	api = (struct sensor_driver_api *)dev->driver_api;
+	const struct sensor_driver_api *api = dev->driver_api;
 
 	return api->sample_fetch(dev, type);
 }
@@ -387,9 +381,7 @@
 				     enum sensor_channel chan,
 				     struct sensor_value *val)
 {
-	struct sensor_driver_api *api;
-
-	api = (struct sensor_driver_api *)dev->driver_api;
+	const struct sensor_driver_api *api = dev->driver_api;
 
 	return api->channel_get(dev, chan, val);
 }