Added missing #include guard.

src/platforms/stm32/usbdfu.h

@@ -17,6 +17,9 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#ifndef __USBDFU_H
+#define __USBDFU_H
+
 #include <libopencm3/usb/usbd.h>
 
 /* Commands sent with wBlockNum == 0 as per ST implementation. */
@@ -44,3 +47,4 @@ void dfu_event(void);
 /* Platform specific function */
 void dfu_detach(void);
 
+#endif /* __USBDFU_H */