mac80211: minstrel_ht: fix sample time check

We need to skip sampling if the next sample time is after jiffies, not before.
This patch fixes an issue where in some cases only very little sampling (or none
at all) is performed, leading to really bad data rates

Fixes: 80d55154

 ("mac80211: minstrel_ht: significantly redesign the rate probing strategy")
Cc: stable@vger.kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20210617103854.61875-1-nbd@nbd.name
Signed-off-by: Johannes Berg <johannes.berg@intel.com>