cfg80211: ocb: Fix null pointer deref if join_ocb is unimplemented

Signed-off-by: Ola Olsson <ola.olsson@sonymobile.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/ocb.c

@@ -29,6 +29,9 @@ int __cfg80211_join_ocb(struct cfg80211_registered_device *rdev,
 	if (dev->ieee80211_ptr->iftype != NL80211_IFTYPE_OCB)
 		return -EOPNOTSUPP;
 
+	if (!rdev->ops->join_ocb)
+		return -EOPNOTSUPP;
+
 	if (WARN_ON(!setup->chandef.chan))
 		return -EINVAL;