mac80211: correct legacy rates check in ieee80211_calc_rx_airtime

There are no legacy rates on 60GHz or sub-1GHz band, so modify the check.

Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: MeiChia Chiu <MeiChia.Chiu@mediatek.com>
Link: https://lore.kernel.org/r/20220308021645.16272-1-MeiChia.Chiu@mediatek.com


[Ghz ->  GHz]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>