Mackie Control: Fix detection of QCon Extenders so 2nd LCD is correct

Logic to detect an extender has to be based on if this surface object is
the master position. Has master fader is true for all surfaces in this
"device".

libs/surfaces/mackie/strip.cc

@@ -129,7 +129,7 @@ Strip::Strip (Surface& s, const std::string& name, int index, const map<Button::
 
 		// The main unit has 9 faders under the second display.
 		// Extenders have 8 faders.
-		if (s.mcp().device_info().has_master_fader()) {
+		if (s.number() == s.mcp().device_info().master_position()) {
 			_lcd2_label_pitch = 6;
 		}
 	}