feat: use any source for expo/weight/offset (#5220)

Co-authored-by: philmoz <phil.a.mitchell@gmail.com>
Co-authored-by: 3djc <3djc@gh.com>
Co-authored-by: elecpower <elecpower@users.noreply.github.com>

radio/src/gui/navigation/common.cpp

@@ -117,6 +117,8 @@ void onSourceLongEnterPress(const char * result)
     }
   } else if (result == STR_MENU_INVERT) {
     checkIncDecSelection = MIXSRC_INVERT;
+  } else if (result == STR_CONSTANT) {
+    checkIncDecSelection = MIXSRC_VALUE;
   }
 }