ath10k: remove ath10k_chanctx struct

In practice there's no point in having a copy of
chanctx_conf.

Most of the time the channel pointer (and band
along with it) is accessed and this can't change
after a chanctx is created because switching is
done using explicit chanctx swapping via
switch_vif_chanctx().

The only thing that can change within a
chanctx_conf and is used by the driver is
radar_enabled and channel width. These are however
always accessed in adequate mac80211 callback
context which guarantees safe access to the
chanctx data.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>