AP_Tuning: adapt to new RC_Channel API

libraries/AP_Tuning/AP_Tuning.cpp

@@ -64,7 +64,7 @@ void AP_Tuning::check_selector_switch(void)
         // no selector switch enabled
         return;
     }
-    RC_Channel *selchan = RC_Channel::rc_channel(selector-1);
+    RC_Channel *selchan = RC_Channels::rc_channel(selector-1);
     if (selchan == nullptr) {
         return;
     }
@@ -172,7 +172,7 @@ void AP_Tuning::check_input(uint8_t flightmode)
         return;
     }
     
-    RC_Channel *chan = RC_Channel::rc_channel(channel-1);
+    RC_Channel *chan = RC_Channels::rc_channel(channel-1);
     if (chan == nullptr) {
         return;
     }