Add return statement on Arduino_LoRaWAN::setFrequency

[olicooper]

Missing return statement on Arduino_LoRaWAN::setFrequency - causes compile errors. Could be related to an earlier issue I raised? https://github.com/mcci-catena/arduino-lorawan/issues/181

[vkynchev]

I can confirm that adding return true; at the end of setFrequency method resolved the core panic on esp32...

[supcik]

I also stumbled on this error

[klauweg]

Since i'm new to esp32/arduino/lorawan/c++ this cost me hours until i found this pull request :-). Why can't it be merged with master soon?

[terrillmoore]

Thanks!