ath9k_hw: move 2g5g switch before nfcal start

During fast channel change, perform 2g5g_switch before starting
noisefloor calibration to avoid nfload timeout.

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