Fix location of avrdude.conf

Marlin/Makefile

@@ -287,7 +287,7 @@ LDFLAGS = -lm
 # Programming support using avrdude. Settings and variables.
 AVRDUDE_PORT = $(UPLOAD_PORT)
 AVRDUDE_WRITE_FLASH = -U flash:w:$(BUILD_DIR)/$(TARGET).hex:i
-AVRDUDE_FLAGS = -D -C $(ARDUINO_INSTALL_DIR)/hardware/tools/avrdude.conf \
+AVRDUDE_FLAGS = -D -C $(ARDUINO_INSTALL_DIR)/hardware/tools/avr/etc/avrdude.conf \
 	-p $(MCU) -P $(AVRDUDE_PORT) -c $(AVRDUDE_PROGRAMMER) \
 	-b $(UPLOAD_RATE)