wifi: mac80211: fix center freq calculation in ieee80211_chandef_downgrade

wifi: mac80211: fix center freq calculation in ieee80211_chandef_downgrade

When mac80211 downgrades working bandwidth, the
center_freq and center_freq1 need to be recalculated.
There is a typo in the case of downgrading bandwidth from
320MHz to 160MHz which would cause a wrong frequency value.

Reviewed-by: Money Wang <Money.Wang@mediatek.com>
Signed-off-by: MeiChia Chiu <MeiChia.Chiu@mediatek.com>
Link: https://lore.kernel.org/r/20220708095823.12959-1-MeiChia.Chiu@mediatek.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>