uas: add stream number sanity checks.

The device uses the guest-supplied stream number unchecked, which can
lead to guest-triggered out-of-band access to the UASDevice->data3 and
UASDevice->status3 fields.  Add the missing checks.

Fixes: CVE-2021-3713
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reported-by: Chen Zhe <chenzhe@huawei.com>
Reported-by: Tan Jingguo <tanjingguo@huawei.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210818120505.1258262-2-kraxel@redhat.com>