[sw] Fix a few non-absolute includes

Signed-off-by: Miguel Young de la Sota <mcyoung@google.com>
diff --git a/sw/device/lib/usb_simpleserial.h b/sw/device/lib/usb_simpleserial.h
index 59f4238..5929c76 100644
--- a/sw/device/lib/usb_simpleserial.h
+++ b/sw/device/lib/usb_simpleserial.h
@@ -9,7 +9,7 @@
 #include <stdint.h>
 
 #include "sw/device/lib/common.h"
-#include "usbdev.h"
+#include "sw/device/lib/usbdev.h"
 
 // This is only here because caller of _init needs it
 typedef struct usb_ss_ctx {