usb: core: hcd: mark expected switch fall-through

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

Addresses-Coverity-ID: 1468266 ("Missing break in switch")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/hcd.c

@@ -2812,6 +2812,7 @@ int usb_add_hcd(struct usb_hcd *hcd,
 	case HCD_USB32:
 		rhdev->rx_lanes = 2;
 		rhdev->tx_lanes = 2;
+		/* fall through */
 	case HCD_USB31:
 		rhdev->speed = USB_SPEED_SUPER_PLUS;
 		break;