stabilize ESP8266 watchdog (sandeepmistry#61)

* stabilize ESP8266 watchdog

* remove guard for ESP8266

* Add brackets

Author: universam1

src/LoRa.cpp

@@ -144,7 +144,9 @@ int LoRaClass::endPacket()
   writeRegister(REG_OP_MODE, MODE_LONG_RANGE_MODE | MODE_TX);
 
   // wait for TX done
-  while((readRegister(REG_IRQ_FLAGS) & IRQ_TX_DONE_MASK) == 0);
+  while ((readRegister(REG_IRQ_FLAGS) & IRQ_TX_DONE_MASK) == 0) {
+    yield();
+  }
 
   // clear IRQ's
   writeRegister(REG_IRQ_FLAGS, IRQ_TX_DONE_MASK);