ar9170usb: add usbid for TP-Link TL-WN821N v2

This patch adds the usbid for TP-Link TL-WN821N v2.

Cc: stable@kernel.org
Reported-by: Fabian Lenz <lenz_fabian@yahoo.de>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>