ath9k: disable RIFS search for AR91xx based chips

While ath9k does not support RIFS yet, the ability to receive RIFS
frames is currently enabled for most chipsets in the initvals.
This is causing baseband related issues on AR9160 and AR9130 based
chipsets, which can lock up under certain conditions.

This patch fixes these issues by overriding the initvals, effectively
disabling RIFS for all affected chipsets.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Cc: stable@kernel.org
Acked-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>