ath9k: Fix IQ calibration

This patch fixes a bug in the TX IQ calibration post
processing routine because of which the driver disables
TX IQ correction even though the calibration results
are valid. This fix is applicable for all chips in the
AR9003 family.

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