ath9k_hw: Fix magnitude/phase coeff correction

Do the magnitude/phase coeff correction only if the outlier
is detected. Updating wrong magnitude/phase coeff factor
impacts not only tx gain setting but also leads to poor
performance in congested networks. In the clear environment
the impact is very minimal because the outlier happens
very rarely according to the past experiment. It occured
less than once every 1000 calibrations.

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