net, wireless: Don't return uninitialized in __cfg80211_stop_sched_scan()

If the 'driver_initiated' function argument to
__cfg80211_stop_sched_scan() is not 0 then we'll return an
uninitialized 'err' from the function.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>