rffrequency: fix cppcheck warnings

Author: cujomalainey

src/TX/Config/ANT_ChannelRfFrequency.h

@@ -21,8 +21,8 @@ class ChannelRfFrequency : public AntRequest {
     uint32_t execute() override;
 #endif // NATIVE_API_AVAILABLE
 private:
-    uint8_t _channel;
-    uint8_t _frequency;
+    uint8_t _channel = 0;
+    uint8_t _frequency = 0;
 };
 
 #endif // ANT_CHANNELRFFREQUENCY_h