iwmc3200wifi: Fix test of unsigned in iwm_ntf_stop_resume_tx()

`queue' was unsigned so the test did not work.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Reviewed-by: Pavel Roskin <proski@gnu.org>
Acked-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>