examples/mqttc: Fix QOS arguments parsing (char->long).

Modify the switch cases in parsearg function for QOS levels definition.
The comparison was made between a long value and a char.

Signed-off-by: Mihai Pacuraru <mpacuraru@protonmail.com>

examples/mqttc/mqttc_pub.c

@@ -192,13 +192,13 @@ static void parsearg(int argc, FAR char *argv[],
           case 'q':
             switch (strtol(optarg, NULL, 10))
               {
-                case '0':
+                case 0L:
                   cfg->qos = MQTT_PUBLISH_QOS_0;
                   break;
-                case '1':
+                case 1L:
                   cfg->qos = MQTT_PUBLISH_QOS_1;
                   break;
-                case '2':
+                case 2L:
                   cfg->qos = MQTT_PUBLISH_QOS_2;
                   break;
                 }