cfg80211: make __cfg80211_join_ibss() static

Function __cfg80211_join_ibss() is only used in net/wireless/ibss.c,
so make it static.

Signed-off-by: Zhao, Gang <gamerh2o@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/wireless/ibss.c b/net/wireless/ibss.c
index 349db9d..a6b5bda 100644
--- a/net/wireless/ibss.c
+++ b/net/wireless/ibss.c
@@ -82,10 +82,10 @@
 }
 EXPORT_SYMBOL(cfg80211_ibss_joined);
 
-int __cfg80211_join_ibss(struct cfg80211_registered_device *rdev,
-			 struct net_device *dev,
-			 struct cfg80211_ibss_params *params,
-			 struct cfg80211_cached_keys *connkeys)
+static int __cfg80211_join_ibss(struct cfg80211_registered_device *rdev,
+				struct net_device *dev,
+				struct cfg80211_ibss_params *params,
+				struct cfg80211_cached_keys *connkeys)
 {
 	struct wireless_dev *wdev = dev->ieee80211_ptr;
 	struct ieee80211_channel *check_chan;