usb: host: xhci: mark expected switch fall-through

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/xhci.c

@@ -4294,6 +4294,7 @@ static unsigned long long xhci_calculate_intel_u1_timeout(
 			break;
 		}
 		/* Otherwise the calculation is the same as isoc eps */
+		/* fall through */
 	case USB_ENDPOINT_XFER_ISOC:
 		timeout_ns = xhci_service_interval_to_ns(desc);
 		timeout_ns = DIV_ROUND_UP_ULL(timeout_ns * 105, 100);