wifi: ath9k: use devm for request_irq()

Avoids having to manually call free_irq(). Simplifies code slightly.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://patch.msgid.link/20240731210243.7467-1-rosenp@gmail.com