mac80211: fix warning: unused variable ifsta

This patch fixes warning unused variable ifsta
when compiling without CONFIG_MAC80211_VERBOSE_DEBUG

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/mlme.c

@@ -366,8 +366,10 @@ static u32 ieee80211_handle_protect_preamb(struct ieee80211_sub_if_data *sdata,
 					   bool use_short_preamble)
 {
 	struct ieee80211_bss_conf *bss_conf = &sdata->bss_conf;
+#ifdef CONFIG_MAC80211_VERBOSE_DEBUG
 	struct ieee80211_if_sta *ifsta = &sdata->u.sta;
 	DECLARE_MAC_BUF(mac);
+#endif
 	u32 changed = 0;
 
 	if (use_protection != bss_conf->use_cts_prot) {