mac80211: Remove unused 'struct rate_control_ref' variable

Commit 3b17fbf8 introduced sta_get_expected_throughput()
leaving variable 'struct rate_control_ref* ref' set but unused.
Compiling with W=1 gives the following warning, fix it.

net/mac80211/sta_info.c: In function ‘sta_set_sinfo’:
net/mac80211/sta_info.c:2052:27: warning: variable ‘ref’ set but not used [-Wunused-but-set-variable]

Fixes: 3b17fbf8 ("mac80211: mesh: Add support for HW RC implementation")
Cc: Johannes Berg <johannes.berg@intel.com>
Cc: Maxim Altshul <maxim.altshul@ti.com>
Signed-off-by: Kirtika Ruchandani <kirtika@google.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/sta_info.c

@@ -2049,16 +2049,12 @@ void sta_set_sinfo(struct sta_info *sta, struct station_info *sinfo)
 {
 	struct ieee80211_sub_if_data *sdata = sta->sdata;
 	struct ieee80211_local *local = sdata->local;
-	struct rate_control_ref *ref = NULL;
 	u32 thr = 0;
 	int i, ac, cpu;
 	struct ieee80211_sta_rx_stats *last_rxstats;
 
 	last_rxstats = sta_get_last_rx_stats(sta);
 
-	if (test_sta_flag(sta, WLAN_STA_RATE_CONTROL))
-		ref = local->rate_ctrl;
-
 	sinfo->generation = sdata->local->sta_generation;
 
 	/* do before driver, so beacon filtering drivers have a