Revert "ath9k: fix ath_tx_process_buffer() potential null ptr dereference"

This reverts commit a56c14bb.

ath_tx_process_buffer() doesn't dereference or check sta and passes it
to ath_tx_complete_aggr() and ath_tx_complete_buf().

ath_tx_complete_aggr() checks the pointer before use. No problem here.

ath_tx_complete_buf() doesn't check or dereference sta and passes it on
to ath_tx_complete(). ath_tx_complete() doesn't check or dereference sta,
but assigns it to tx_info->status.status_driver_data[0]

ath_tx_complete_buf() is called from ath_tx_complete_aggr() passing
null ieee80211_sta pointer.

There is a potential for dereference later on, if and when the
tx_info->status.status_driver_data[0]is referenced. In addition, the
rcu read lock might be released before referencing the contents.

ath_tx_complete_buf() should be fixed to check sta perhaps? Worth
looking into.

Reverting this patch because it doesn't solve the problem and introduces
memory leak by skipping buffer completion if the pointer (sta) is NULL.

Fixes: a56c14bb

 ("ath9k: fix ath_tx_process_buffer() potential null ptr dereference")
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210217211801.22540-1-skhan@linuxfoundation.org