ath9k_hw: make sure PAPRD training is properly done

checking the status of PAPRD_AGC2_POWER(Log(ADC_power) measured after
last gain-change in dB) field suggests whether the PAPRD is completely/properly
done. This is an additional check apart from polling for PAPRD done bit being set.
        Susinder suggests that the ideal power range value should be
0xf0 to 0xfe. With AR9382 we do have the values in this range. to have a
common check for all platforms we take agc2_power should be atleast greater
than 0xe0

Cc: susinder@qca.qualcomm.com
Cc: senthilb@qca.qualcomm.com
Cc: kmuthusa@qca.qualcomm.com
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>