Minor cut-n-paste typo in comment

PaulSchulz · web-flow · commit d008524eb9ee · 2023-03-07T16:03:31.000+10:30
US915 instead of AU915
diff --git a/src/Arduino_LoRaWAN_ttn.h b/src/Arduino_LoRaWAN_ttn.h
@@ -123,7 +123,7 @@ class Arduino_LoRaWAN_ttn_au915 : public Arduino_LoRaWAN_ttn_base
         // select the subband.
         virtual void NetBeginRegionInit();
 
-        // Implement the NetJoin() operations for US915
+        // Implement the NetJoin() operations for AU915
         virtual void NetJoin();
 
 private:
