wifi: rtw89: fix null vif pointer when get management frame date rate

When transmitting a packet that gets from ieee80211_nullfunc_get(),
the vif in tx_info->control was no assigned, which will cause
dereferencing a null pointer.
Signed-off-by: Kuan-Chung Chen <damon.chen@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230106121517.19841-1-pkshih@realtek.com

drivers/net/wireless/realtek/rtw89/core.c

@@ -498,7 +498,8 @@ static u16 rtw89_core_get_mgmt_rate(struct rtw89_dev *rtwdev,
 	const struct rtw89_chan *chan = rtw89_chan_get(rtwdev, RTW89_SUB_ENTITY_0);
 	u16 lowest_rate;
 
-	if (tx_info->flags & IEEE80211_TX_CTL_NO_CCK_RATE || vif->p2p)
+	if (tx_info->flags & IEEE80211_TX_CTL_NO_CCK_RATE ||
+	    (vif && vif->p2p))
 		lowest_rate = RTW89_HW_RATE_OFDM6;
 	else if (chan->band_type == RTW89_BAND_2G)
 		lowest_rate = RTW89_HW_RATE_CCK1;