The struct ath5k_hw member ah_txq_isr_txok_all is never reset/assigned
outside of ath5k_hw_get_isr() and with the used bitwise-or in the
interrupt handling accumulates all ever set interrupt flags.

Fix this by clearing ah_txq_isr_txok_all before assigning.

Patch tested with Senao NMP-8602 card

  Qualcomm Atheros AR5413/AR5414 Wireless Network Adapter [AR5006X(S) 802.11abg] (rev 01)
  ath5k: phy6: Atheros AR5413 chip found (MAC: 0xa4, PHY: 0x61)

running IBSS mode against Atheros (ath9k) card using
ping and iperf traffic.
Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20220110223021.17655-5-ps.report@gmx.net