ath9k: Check explicitly for IQ calibration

In chips like AR955x, the initvals contain the information
whether IQ calibration is to be done in the HW when an
AGC calibration is triggered. Check if IQ-CAL is enabled
in the initvals before flagging 'txiqcal_done' as true.

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