Update and fix CHDK

Marlin/src/gcode/gcode.cpp

@@ -522,7 +522,7 @@ void GcodeSuite::process_parsed_command(
         case 304: M304(); break;                                  // M304: Set bed PID parameters
       #endif
 
-      #if defined(CHDK) || HAS_PHOTOGRAPH
+      #if PIN_EXISTS(CHDK) || HAS_PHOTOGRAPH
         case 240: M240(); break;                                  // M240: Trigger a camera by emulating a Canon RC-1 : http://www.doc-diy.net/photo/rc-1_hacked/
       #endif