USB: mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/renesas_usbhs/mod_gadget.c

@@ -502,6 +502,7 @@ static int usbhsg_irq_ctrl_stage(struct usbhs_priv *priv,
 	case READ_STATUS_STAGE:
 	case WRITE_STATUS_STAGE:
 		usbhs_dcp_control_transfer_done(pipe);
+		/* fall through */
 	default:
 		return ret;
 	}