Add parenthesis to fix compiler warning

Gcc warns when using = where == seems logical, and adding parenthesis
tells gcc you really mean =.

Author: matthijskooijman

examples/mqtt_cc3k/mqtt_cc3k.ino

@@ -121,7 +121,7 @@ void loop() {
 
   // this is our 'wait for incoming subscription packets' busy subloop
   Adafruit_MQTT_Subscribe *subscription;
-  while (subscription = mqtt.readSubscription(1000)) {
+  while ((subscription = mqtt.readSubscription(1000))) {
     if (subscription == &onoffbutton) {
       Serial.print(F("Got: "));
       Serial.println((char *)onoffbutton.lastread);

examples/mqtt_esp8266/mqtt_esp8266.ino

@@ -104,7 +104,7 @@ void loop() {
 
   // this is our 'wait for incoming subscription packets' busy subloop
   Adafruit_MQTT_Subscribe *subscription;
-  while (subscription = mqtt.readSubscription(1000)) {
+  while ((subscription = mqtt.readSubscription(1000))) {
     if (subscription == &onoffbutton) {
       Serial.print(F("Got: "));
       Serial.println((char *)onoffbutton.lastread);

examples/mqtt_fona/mqtt_fona.ino

@@ -144,7 +144,7 @@ void loop() {
 
   // this is our 'wait for incoming subscription packets' busy subloop
   Adafruit_MQTT_Subscribe *subscription;
-  while (subscription = mqtt.readSubscription(5000)) {
+  while ((subscription = mqtt.readSubscription(5000))) {
     if (subscription == &onoffbutton) {
       Serial.print(F("Got: "));
       Serial.println((char *)onoffbutton.lastread);