mac80211: make rate_control_alloc static

rate_control_alloc is not used by anything outside of
ieee80211_init_rate_ctrl_alg.  Both are in rate.c; there's no reason to make
rate_control_alloc visible outside of it.

Signed-off-by: Andres Salomon <dilinger@collabora.co.uk>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/rate.c

@@ -145,7 +145,7 @@ static const struct file_operations rcname_ops = {
 };
 #endif
 
-struct rate_control_ref *rate_control_alloc(const char *name,
+static struct rate_control_ref *rate_control_alloc(const char *name,
 					    struct ieee80211_local *local)
 {
 	struct dentry *debugfsdir = NULL;