wifi: brcmfmac: fix potential memory leak in brcmf_netdev_start_xmit()

The brcmf_netdev_start_xmit() returns NETDEV_TX_OK without freeing skb
in case of pskb_expand_head() fails, add dev_kfree_skb() to fix it.
Compile tested only.

Fixes: 270a6c1f ("brcmfmac: rework headroom check in .start_xmit()")
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>
Reviewed-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/1668684782-47422-1-git-send-email-zhangchangzhong@huawei.com

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

@@ -336,6 +336,7 @@ static netdev_tx_t brcmf_netdev_start_xmit(struct sk_buff *skb,
 			bphy_err(drvr, "%s: failed to expand headroom\n",
 				 brcmf_ifname(ifp));
 			atomic_inc(&drvr->bus_if->stats.pktcow_failed);
+			dev_kfree_skb(skb);
 			goto done;
 		}
 	}