drivers:net:wireless:mediatek: fix build warning

drivers/net/wireless/mediatek/mt76/mt7921/main.c: In function 'mt7921_get_et_stats':
drivers/net/wireless/mediatek/mt76/mt7921/main.c:1024:26: warning: format '%lu' expects argument of type 'long unsigned int', but argument 4 has type 'unsigned int' [-Wformat=]
   dev_err(dev->mt76.dev, "ei: %d  SSTATS_LEN: %lu",

Signed-off-by: Wang Haojun <wanghaojun@loongson.cn>

drivers/net/wireless/mediatek/mt76/mt7921/main.c

@@ -1021,7 +1021,7 @@ void mt7921_get_et_stats(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
 
 	ei += wi.worker_stat_count;
 	if (ei != ARRAY_SIZE(mt7921_gstrings_stats))
-		dev_err(dev->mt76.dev, "ei: %d  SSTATS_LEN: %lu",
+		dev_err(dev->mt76.dev, "ei: %d  SSTATS_LEN: %u",
 			ei, ARRAY_SIZE(mt7921_gstrings_stats));
 }