MLK-21161-02 brcmfmac: validate ifp pointer in brcmf_txfinalize

We got ifp null pointer kernel panic in brcmf_txfinalize after removing
Wi-Fi USB dongle when data was transmitting, The root cause is that
interface was removed before calling brcmf_txfinalize in
brcmf_fws_dequeue_worker and finally caused kernel panic.

Signed-off-by: Wright Feng <wright.feng@cypress.com>
Signed-off-by: Fugang Duan <fugang.duan@nxp.com>

drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c

@@ -370,6 +370,11 @@ void brcmf_txfinalize(struct brcmf_if *ifp, struct sk_buff *txp, bool success)
 	struct ethhdr *eh;
 	u16 type;
 
+	if (!ifp) {
+		brcmu_pkt_buf_free_skb(txp);
+		return;
+	}
+
 	eh = (struct ethhdr *)(txp->data);
 	type = ntohs(eh->h_proto);