mac80211: airtime: Fix an off by one in ieee80211_calc_rx_airtime()

This code was copied from mt76 and inherited an off by one bug from
there. The > should be >= so that we don't read one element beyond
the end of the array.

Fixes: db3e1c40cf2f ("mac80211: Import airtime calculation code from mt76")
Reported-by: Toke Høiland-Jørgensen <[e-mail]>
Signed-off-by: Dan Carpenter <[e-mail]>
Acked-by: Toke Høiland-Jørgensen <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Johannes Berg <[e-mail]>

net/mac80211/airtime.c

···
 			return 0;
 
 		sband = hw->wiphy->bands[status->band];
-		if (!sband || status->rate_idx > sband->n_bitrates)
+		if (!sband || status->rate_idx >= sband->n_bitrates)
 			return 0;
 
 		rate = &sband->bitrates[status->rate_idx];