usb: misc: usbtest: usbtest_do_ioctl may return positive integer

For case 14 and case 21, their correct return value is the number
of bytes transferred, so it is a positive integer. But in usbtest_ioctl,
it takes non-zero as false return value for usbtest_do_ioctl, so
it will treat the correct test as wrong test, then the time on
tests will be the minus value.

Signed-off-by: Peter Chen <peter.chen@nxp.com>
Cc: stable <stable@vger.kernel.org>
Fixes: 18fc4eb ("usb: misc: usbtest: Remove timeval usage")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/misc/usbtest.c

@@ -2602,7 +2602,7 @@ usbtest_ioctl(struct usb_interface *intf, unsigned int code, void *buf)
 	ktime_get_ts64(&start);
 
 	retval = usbtest_do_ioctl(intf, param_32);
-	if (retval)
+	if (retval < 0)
 		goto free_mutex;
 
 	ktime_get_ts64(&end);