cfg80211: remove regulatory_update()

regulatory_update() just calls wiphy_update_regulatory().
wiphy_update_regulatory() assumes you already have
the reg_mutex held so just move the call within locking
context and kill the superfluous regulatory_update().

Signed-off-by: Luis R. Rodriguez <mcgrof@qca.qualcomm.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>