ath9k: dynack: move debug log after buffer increments

Move debug log in ath_dynack_sample_tx_ts and ath_dynack_sample_ack_ts
after timestamp buffer head/tail increments in order to make debugging
more user friendly

Tested-by: Koen Vandeputte <koen.vandeputte@ncentric.com>
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>