usb/usbtest: fix test10 on superpseed

dummy_hcd + g_zero:

|./testusb -a -s 1024 -v 1024 -t 10
| usbtest 2-1:3.0: subtest 14 error, status 0

with patch:
  ./testusb -a -t 10
|unknown speed   /proc/bus/usb/001/002
| dummy_udc dummy_udc: disabled ep-a
| dummy_udc dummy_udc: disabled ep-b
| dummy_udc dummy_udc: enabled ep-a (ep1in-bulk) maxpacket 1024
| dummy_udc dummy_udc: enabled ep-b (ep2out-bulk) maxpacket 1024
| zero gadget: source/sink enabled
| usbtest 1-1:3.0: TEST 10:  queue 32 control calls, 1000 times
| dummy_hcd dummy_hcd: timer fired with no URBs pending?
|/proc/bus/usb/001/002 test 10,    0.022370 secs

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/misc/usbtest.c

@@ -1030,6 +1030,8 @@ test_ctrl_queue(struct usbtest_dev *dev, struct usbtest_param *param)
 			req.wValue = cpu_to_le16((USB_DT_DEVICE << 8) | 0);
 			/* device descriptor size == 18 bytes */
 			len = udev->descriptor.bMaxPacketSize0;
+			if (udev->speed == USB_SPEED_SUPER)
+				len = 512;
 			switch (len) {
 			case 8:
 				len = 24;