MAINTAINERS: wifi: ath12k: add wiki link

The ath12k wireless driver now has a wiki, so advertise it.

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230829-ath12kwiki-v1-1-df37127527a1@quicinc.com