mac80211: minstrel_ht: fix per-group max throughput rate initialization

mac80211: minstrel_ht: fix per-group max throughput rate initialization

BugLink: https://bugs.launchpad.net/bugs/1863019
[ Upstream commit 56dd918ff06e3ee24d8067e93ed12b2a39e71394 ]

The group number needs to be multiplied by the number of rates per group
to get the full rate index

Fixes: 5935839ad735 ("mac80211: improve minstrel_ht rate sorting by throughput & probability")
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20190820095449.45255-1-nbd@nbd.name
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>