ath9k: add missing AR9340 in ath_mac_bb_names

AR9340 is not listed in ath_mac_bb_names, which leads to such a message:
ieee80211 phy0: Atheros AR???? Rev:0 mem=0xb8100000, irq=2

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>