sandbox: Enable USB keyboard

Enable the USB keyboard on sandbox, now that we have a suitable emulation
driver.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/configs/sandbox.h b/include/configs/sandbox.h
index fb1bfb7..1c75c38 100644
--- a/include/configs/sandbox.h
+++ b/include/configs/sandbox.h
@@ -177,7 +177,7 @@
 
 #define CONFIG_KEYBOARD
 
-#define SANDBOX_SERIAL_SETTINGS		"stdin=serial,cros-ec-keyb\0" \
+#define SANDBOX_SERIAL_SETTINGS		"stdin=serial,cros-ec-keyb,usbkbd\0" \
 					"stdout=serial,lcd\0" \
 					"stderr=serial,lcd\0"
 #else