Rename 'atheros' target to more precise 'ath25'.

Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@44736 3c298f89-4303-0410-b956-a3cf2f4a3e73