usb: class: usbtmc: 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/class/usbtmc.c

@@ -1343,6 +1343,7 @@ static void usbtmc_interrupt(struct urb *urb)
 	case -EOVERFLOW:
 		dev_err(dev, "overflow with length %d, actual length is %d\n",
 			data->iin_wMaxPacketSize, urb->actual_length);
+		/* fall through */
 	case -ECONNRESET:
 	case -ENOENT:
 	case -ESHUTDOWN: