ar9170: wrong test on outlen in ar9170_usb_exec_cmd() ?

remove redundant test: outlen is unsigned

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Acked-by: Christian Lamparter <chunkeey@web.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>