mac80211: Clarify ath9k & ath10k debug selection

Ath debug mode applies to ath10k as well as ath9k.
Update Makefile help text to clarify.

Signed-off-by: Kevin Darbyshire-Bryant <kevin@darbyshire-bryant.me.uk>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46468 3c298f89-4303-0410-b956-a3cf2f4a3e73