DFU: make sure to properly initialize g_dfu pointer before using it
diff --git a/firmware/atmel_softpack_libraries/usb/device/dfu/dfu.h b/firmware/atmel_softpack_libraries/usb/device/dfu/dfu.h
index dd0e5e2..4af3e3b 100644
--- a/firmware/atmel_softpack_libraries/usb/device/dfu/dfu.h
+++ b/firmware/atmel_softpack_libraries/usb/device/dfu/dfu.h
@@ -97,6 +97,8 @@
 	unsigned int total_bytes;
 };
 
+/* RAM address for this magic value above */
+extern struct dfudata _g_dfu;
 extern struct dfudata *g_dfu;
 
 void set_usb_serial_str(const uint8_t *serial_usbstr);