hostapd:  Fix crash when scan fails.

When scan failed, the wpa_driver_nl80211_scan method tried
to recursively call itself, but it passed in the wrong argument
for the void*, and so then it crashed accessing bad memory.

With this fix, hostapd still will not retry the scan later, but
at least it will exit cleanly and won't polute the file system
with core files.

Signed-off-by: Ben Greear <greearb@candelatech.com>