Revert "ath9k_hw: Update rx gain initval to improve rx sensitivity"

This reverts commit 68d9e1fa

This change reduces rx sensitivity with no apparent extra benefit.
It looks like it was meant for testing in a specific scenario,
but it was never properly validated.

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