ath10k: Fix a use after free in ath10k_htc_send_bundle

In ath10k_htc_send_bundle, the bundle_skb could be freed by
dev_kfree_skb_any(bundle_skb). But the bundle_skb is used later
by bundle_skb->len.

As skb_len = bundle_skb->len, my patch replaces bundle_skb->len to
skb_len after the bundle_skb was freed.

Fixes: c8334512 ("ath10k: add htt TX bundle for sdio")
Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210329120154.8963-1-lyl2019@mail.ustc.edu.cn