ath5k: remove unused ah_txq_isr_qtrig member from struct ath5k_hw

Remove unused ah_txq_isr_qtrig member from struct ath5k_hw (set in
ath5k_hw_get_isr() but never used anywhere).

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20220110223021.17655-1-ps.report@gmx.net