ath10k: Acquire tx_lock in tx error paths

ath10k_htt_tx_free_msdu_id() has a lockdep assertion that htt->tx_lock
is held. Acquire the lock in a couple of error paths when calling that
function to ensure this condition is met.

Fixes: 6421969f ("ath10k: refactor tx pending management")
Fixes: e62ee5c3

 ("ath10k: Add support for htt_data_tx_desc_64 descriptor")
Signed-off-by: Evan Green <evgreen@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200604105901.1.I5b8b0c7ee0d3e51a73248975a9da61401b8f3900@changeid