ath9k: remove a lock to fix a deadlock on hw reset

git-svn-id: svn://svn.openwrt.org/openwrt@35147 3c298f89-4303-0410-b956-a3cf2f4a3e73
ath9k: remove a lock to fix a deadlock on hw reset

Backport of r35147

git-svn-id: svn://svn.openwrt.org/openwrt@35148 3c298f89-4303-0410-b956-a3cf2f4a3e73