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

This reverts commit 68d9e1fa24d9c7c2e527f49df8d18fb8cf0ec943

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>