ath9k: fix handling of the default chip pci id on ar93xx (#14886)

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39432 3c298f89-4303-0410-b956-a3cf2f4a3e73