ath9k: Fix XLNA bias strength

The EEPROM parameter to determine whether the bias
strength values for XLNA have to be applied is part
of the miscConfiguration field and not featureEnable.

Cc: stable@vger.kernel.org
Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>