feat: Add support for Radiomaster MT12 (#4277)

Co-authored-by: 3djc <lesitewebdejc@hotmail.com>
Co-authored-by: raphaelcoeffic <1050031+raphaelcoeffic@users.noreply.github.com>
Co-authored-by: Peter Feerick <peter.feerick@gmail.com>

radio/src/mixer.cpp

@@ -460,10 +460,10 @@ getvalue_t getValue(mixsrc_t i, bool* valid)
       default:
         return telemetryItem.value;
     }
-  } else {
-    if (valid != nullptr) *valid = false;
-    return 0;
   }
+  
+  if (valid != nullptr) *valid = false;
+  return 0;
 }
 
 void evalTrims()