Fix CALIBRATION_GCODE pin handling

Marlin/src/pins/sam/pins_CNCONTROLS_15D.h

@@ -1,3 +1,25 @@
+/**
+ * Marlin 3D Printer Firmware
+ * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
 /**
  * CNControls V15 for HMS434 with DUE pin assignments
  */
@@ -92,6 +114,10 @@
 //#define PWM_2_PIN          13
 //#define SPARE_IO           17
 #define BEEPER_PIN         13
-#define CALIBRATION_PIN    66
 #define STAT_LED_BLUE_PIN  -1
 #define STAT_LED_RED_PIN   31
+
+// G425 CALIBRATION_GCODE default pin
+#ifndef CALIBRATION_PIN
+  #define CALIBRATION_PIN  66
+#endif