ath10k: fix rx_channel during hw reconfigure

Upon firmware assert, restart work will be triggered so that mac80211
will reconfigure the driver. An issue is reported that after restart
work, survey dump data do not contain in-use (SURVEY_INFO_IN_USE) info
for operating channel. During reconfigure, since mac80211 already has
valid channel context for given radio, channel context iteration return
num_chanctx > 0. Hence rx_channel is always NULL. Fix this by assigning
channel context to rx_channel when driver restart is in progress.

Cc: stable@vger.kernel.org
Signed-off-by: Rajkumar Manoharan <rmanohar@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>