wifi: ath9k: reset survey of current channel after a scan started

In the `ath_set_channel()` function, we only reset surveys that are not
from the current channel. This leads to the accumulation of survey data for
the current channel indefinitely. This may not be the most optimal
approach, as we want the ACS to rely on the most recent survey.
So reset the survey data for the current channel at the start of each scan.

Signed-off-by: Hancheng Yang <hyang@freebox.fr>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20231205170623.3029689-1-hyang@freebox.fr