Fix build on Sanguino based boards with ATmega1284P

Marlin/pins.h

@@ -475,8 +475,10 @@
 #define KNOWN_BOARD 1
 
 #ifndef __AVR_ATmega644P__
+#ifndef __AVR_ATmega1284P__
 #error Oops!  Make sure you have 'Sanguino' selected from the 'Tools -> Boards' menu.
 #endif
+#endif
 
 //x axis pins
     #define X_STEP_PIN      15
@@ -546,8 +548,10 @@
 #if MOTHERBOARD == 6
 #define KNOWN_BOARD 1
 #ifndef __AVR_ATmega644P__
+#ifndef __AVR_ATmega1284P__
 #error Oops!  Make sure you have 'Sanguino' selected from the 'Tools -> Boards' menu.
 #endif
+#endif
 
 #define X_STEP_PIN         15
 #define X_DIR_PIN          21
@@ -867,8 +871,10 @@
 #define MOTHERBOARD 6
 #define KNOWN_BOARD 1
 #ifndef __AVR_ATmega644P__
+#ifndef __AVR_ATmega1284P__
 #error Oops!  Make sure you have 'Sanguino' selected from the 'Tools -> Boards' menu.
 #endif
+#endif
 
 #define X_STEP_PIN         15
 #define X_DIR_PIN          18