usb: gadget: thor: Invoke board specific USB cleanup interface

This patch invokes board-specific USB cleanup (board_usb_cleanup)
function in the thor gadget.

Signed-off-by: Inha Song <ideal.song@samsung.com>
diff --git a/common/cmd_thordown.c b/common/cmd_thordown.c
index 8ed1dc6..436b7f5 100644
--- a/common/cmd_thordown.c
+++ b/common/cmd_thordown.c
@@ -56,6 +56,7 @@
 
 exit:
 	g_dnl_unregister();
+	board_usb_cleanup(controller_index, USB_INIT_DEVICE);
 done:
 	dfu_free_entities();