mt76: mt7915: fix sta_rec_wtbl tag len

Fix tag len error for sta_rec_wtbl, which causes fw parsing error for
the tags placed behind it.

Fixes: e57b7901 ("mt76: add mac80211 driver for MT7915 PCIe-based chipsets")
Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7915/mcu.c

@@ -622,7 +622,7 @@ mt7915_mcu_alloc_wtbl_req(struct mt7915_dev *dev, struct mt7915_sta *msta,
 	}
 
 	if (sta_hdr)
-		sta_hdr->len = cpu_to_le16(sizeof(hdr));
+		le16_add_cpu(&sta_hdr->len, sizeof(hdr));
 
 	return skb_put_data(nskb, &hdr, sizeof(hdr));
 }