ath5k: fix ah_txq_isr_txok_all setting

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

drivers/net/wireless/ath/ath5k/dma.c

@@ -650,6 +650,7 @@ ath5k_hw_get_isr(struct ath5k_hw *ah, enum ath5k_int *interrupt_mask)
 		 */
 		*interrupt_mask = (pisr & AR5K_INT_COMMON) & ah->ah_imr;
 
+		ah->ah_txq_isr_txok_all = 0;
 
 		/* We treat TXOK,TXDESC, TXERR and TXEOL
 		 * the same way (schedule the tx tasklet)