wifi: ath9k: Fix potential array-index-out-of-bounds read in ath9k_htc_txstatus()

Fix an array-index-out-of-bounds read in ath9k_htc_txstatus(). The bug
occurs when txs->cnt, data from a URB provided by a USB device, is
bigger than the size of the array txs->txstatus, which is
HTC_MAX_TX_STATUS. WARN_ON() already checks it, but there is no bug
handling code after the check. Make the function return if that is the
case.

Found by a modified version of syzkaller.

UBSAN: array-index-out-of-bounds in htc_drv_txrx.c
index 13 is out of range for type '__wmi_event_txstatus [12]'
Call Trace:
 ath9k_htc_txstatus
 ath9k_wmi_event_tasklet
 tasklet_action_common
 __do_softirq
 irq_exit_rxu
 sysvec_apic_timer_interrupt

Signed-off-by: Minsuk Kang <linuxlovemin@yonsei.ac.kr>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20231113065756.1491991-1-linuxlovemin@yonsei.ac.kr