MAINTAINERS: ath9k: add git tree

ath9k patches go to my ath.git tree, document that.

Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230614144704.505553-2-kvalo@kernel.org

MAINTAINERS

@@ -17371,6 +17371,7 @@ M:	Toke Høiland-Jørgensen <toke@toke.dk>
 L:	linux-wireless@vger.kernel.org
 S:	Maintained
 W:	https://wireless.wiki.kernel.org/en/users/Drivers/ath9k
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git
 F:	Documentation/devicetree/bindings/net/wireless/qca,ath9k.yaml
 F:	drivers/net/wireless/ath/ath9k/