mac80211: fix ieee80211_he_oper_size() comment

Johannes mentioned that the comment should not reference mac80211 as other
subsystems might call the helper.

Signed-off-by: John Crispin <john@phrozen.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20190729102342.8659-1-john@phrozen.org


Signed-off-by: Johannes Berg <johannes.berg@intel.com>