[sw] Promulgate better use of standard headers.

Signed-off-by: Miguel Young de la Sota <mcyoung@google.com>
diff --git a/sw/device/lib/usb_simpleserial.c b/sw/device/lib/usb_simpleserial.c
index 3de162f..3ce3f8d 100644
--- a/sw/device/lib/usb_simpleserial.c
+++ b/sw/device/lib/usb_simpleserial.c
@@ -2,11 +2,10 @@
 // Licensed under the Apache License, Version 2.0, see LICENSE for details.
 // SPDX-License-Identifier: Apache-2.0
 
-// Get NULL from here
-#include "usb_simpleserial.h"
+#include "sw/device/lib/usb_simpleserial.h"
 
 #include "sw/device/lib/common.h"
-#include "usbdev.h"
+#include "sw/device/lib/usbdev.h"
 
 #define MAX_GATHER 16