wifi: ath11k: refactor transmitted arvif retrieval

wifi: ath11k: refactor transmitted arvif retrieval

Create a new function ath11k_mac_get_tx_arvif() to retrieve 'arvif'
for the transmitted interface of the MBSSID set. This will help
modifying the same code path to reflect mac80211 data structure
changes to support MLO. This also fixes an issue in
ath11k_mac_update_vif_chan() where tx_arvif is not reset to NULL
inside for loop during each iteration. Compile tested only.

Signed-off-by: Aloka Dixit <aloka.dixit@oss.qualcomm.com>
Reviewed-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Link: https://patch.msgid.link/20250210182718.408891-2-aloka.dixit@oss.qualcomm.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>