wimax: usb-tx: mark expected switch fall-through

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

Notice that in this particular case, I placed the "fall through"
annotation at the bottom of the case, which is what GCC is expecting
to find.

Addresses-Coverity-ID: 115075 ("Missing break in switch")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/wimax/i2400m/usb-tx.c

@@ -131,12 +131,12 @@ retry:
 			dev_err(dev, "BM-CMD: too many stalls in "
 				"URB; resetting device\n");
 			usb_queue_reset_device(i2400mu->usb_iface);
-			/* fallthrough */
 		} else {
 			usb_clear_halt(i2400mu->usb_dev, usb_pipe);
 			msleep(10);	/* give the device some time */
 			goto retry;
 		}
+		/* fall through */
 	case -EINVAL:			/* while removing driver */
 	case -ENODEV:			/* dev disconnect ... */
 	case -ENOENT:			/* just ignore it */