mac80211: Fix pid rate-setting algorithm to allow rate changes

In commit 9ea2c74 named "mac80211/drivers: rewrite the rate control API",
the meaning of status.rates[i].count was changed from number of retries
to total number of tries. As a result, the pid rate-setting algorithm fails
because every packet appears to have needed a retransmit.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>