wifi: ath11k: Consistently use ath11k_vif_to_arvif()

Helper function ath11k_vif_to_arvif() exists to retrieve a struct
ath11k_vif from a struct ieee80211_vif. However, in multiple places
this logic is open-coded with inline typecasting. Since the
typecasting prevents the compiler from type-checking the source and
destination, update the driver to consistently use the helper
function.

No functional changes, compile tested only.

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230821-ath11k_vif_to_arvif-v1-1-fa2c3b60b5cf@quicinc.com