usb_device.h: Add missing header guards

BUG=b:143389556
BRANCH=none
TEST=builds

Change-Id: If7b480e213ba9c87e90ff6a69696c65280988cfb
Signed-off-by: Edward O'Callaghan <quasisec@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/flashrom/+/2032908
Tested-by: Edward O'Callaghan <quasisec@chromium.org>
Commit-Queue: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-by: Sam McNally <sammc@chromium.org>
diff --git a/usb_device.h b/usb_device.h
index 5756f52..54383fb 100644
--- a/usb_device.h
+++ b/usb_device.h
@@ -14,6 +14,9 @@
  * GNU General Public License for more details.
  */
 
+#ifndef USB_DEVICE_H
+#define USB_DEVICE_H
+
 /*
  * USB device matching framework
  *
@@ -157,3 +160,5 @@
  *     The next device in the device list.
  */
 struct usb_device *usb_device_free(struct usb_device *device);
+
+#endif /* USB_DEVICE_H */