mac80211: Fix AP mode regression

Commit mac80211: avoid using synchronize_rcu in ieee80211_set_probe_resp
changed the return value when the probe response template is not present.
Revert to the earlier value of 1 - this fixes AP mode for drivers like
ath9k.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>