mac80211_hwsim: treat as part of mac80211 for MAINTAINERS

Since I maintain this driver as part of mac80211, add it to
the file list for mac80211; this helps submitters send it to
me instead of Kalle and also makes the build robot apply the
patches for it on the right tree for build attempts.

Acked-by: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>