cfg80211: fix station info handling bugs

Fix two places where the structure isn't initialized to zero,
and thus can't be filled properly by the driver.

Fixes: 4a4b8169 ("cfg80211: Accept multiple RSSI thresholds for CQM")
Fixes: 9930380f ("cfg80211: implement IWRATE")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>