nl80211: Uninitialized variable

There is a path in nl80211_set_wiphy where result is tested but
uninitialized.

I am hitting this path when I attempt:

sh# iw dev wlan0 set channel 10
command failed: Unknown error 1069727332 (-1069727332)

Signed-off-by: William Jordan <bjordan@rajant.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>