usb: usbtest: Remove stack VLA usage

The kernel would like to have all stack VLA usage removed[1].  We
already have a pre-processor constant defined MAX_SGLEN.  We can use
this instead of the variable param-sglen.

[1]: https://lkml.org/lkml/2018/3/7/621Signed-off-by: Tobin C. Harding <me@tobin.cc>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/misc/usbtest.c

@@ -2028,11 +2028,14 @@ test_queue(struct usbtest_dev *dev, struct usbtest_param_32 *param,
 	unsigned		i;
 	unsigned long		packets = 0;
 	int			status = 0;
-	struct urb		*urbs[param->sglen];
+	struct urb		*urbs[MAX_SGLEN];
 
 	if (!param->sglen || param->iterations > UINT_MAX / param->sglen)
 		return -EINVAL;
 
+	if (param->sglen > MAX_SGLEN)
+		return -EINVAL;
+
 	memset(&context, 0, sizeof(context));
 	context.count = param->iterations * param->sglen;
 	context.dev = dev;