ath9k: disable unnecessary PHY error reporting

PHY errors relevant for ANI are always tracked by hardware counters, the
bits that allow them to pass through the rx filter are independent of that.
Enabling PHY errors in the rx filter often creates lots of useless DMA traffic
and might be responsible for some of the rx dma stop failure warnings.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Cc: stable@kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>