Several mqtt documentation fixes found by clang

src/include/lwip/apps/mqtt.h

@@ -114,7 +114,6 @@ enum {
  * Function prototype for MQTT incoming publish data callback function. Called when data
  * arrives to a subscribed topic @see mqtt_subscribe
  *
- * @param client MQTT client itself
  * @param arg Additional argument to pass to the callback function
  * @param data User data, pointed object, data may not be referenced after callback return,
           NULL is passed when all publish data are delivered
@@ -130,11 +129,9 @@ typedef void (*mqtt_incoming_data_cb_t)(void *arg, const u8_t *data, u16_t len,
  * Function prototype for MQTT incoming publish function. Called when an incoming publish
  * arrives to a subscribed topic @see mqtt_subscribe
  *
- * @param client MQTT client itself
  * @param arg Additional argument to pass to the callback function
  * @param topic Zero terminated Topic text string, topic may not be referenced after callback return
  * @param tot_len Total length of publish data, if set to 0 (no publish payload) data callback will not be invoked
- * @return Optional numerical topic identifier to be used in data callback
  */
 typedef void (*mqtt_incoming_publish_cb_t)(void *arg, const char *topic, u32_t tot_len);