wifi: ath9k: convert msecs to jiffies where needed

Since 'ieee80211_queue_delayed_work()' expects timeout in
jiffies and not milliseconds, 'msecs_to_jiffies()' should
be used in 'ath_restart_work()' and '__ath9k_flush()'.

Fixes: d63ffc45 ("ath9k: rename tx_complete_work to hw_check_work")
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230613134655.248728-1-dmantipov@yandex.ru