fix for idf 5.2.1

[mhaberler]

not sure this is the proper way, but works for me:

/Users/mah/Ballon/src/BalloonWare/esp32-ble2mqtt/main/mqtt.c: In function 'mqtt_subscribe':
/Users/mah/esp/v5.2.1-git/components/mqtt/esp-mqtt/include/mqtt_client.h:464:84: error: '_Generic' selector of type 'const char *' is not compatible with any association
  464 | #define esp_mqtt_client_subscribe(client_handle, topic_type, qos_or_size) _Generic((topic_type), \
      |                                                                                    ^
/Users/mah/Ballon/src/BalloonWare/esp32-ble2mqtt/main/mqtt.c:165:9: note: in expansion of macro 'esp_mqtt_client_subscribe'
  165 |     if (esp_mqtt_client_subscribe(mqtt_handle, topic, qos) < 0)
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~

[shmuelzon]

Hey, there were some additional things that needed handling to fully support ESP-IDF v5.2.1. I've added them in #199.
For what it's worth, your modification for the MQTT API was the same one I opted for :)

[mhaberler]

yeah, had never heard of _Generic() before

appreciated - will give it a spin!

edit: works perfectly.