ath9k_hw: Fix noise floor calibration timeout on fast channel change

During the fast channel change noise floor values are being loaded
twice at init_cal and after channel_change. The commit "ath9k_hw:
Improve fast channel change for AR9003 chips" overlooked it that
caused failure to load nf while doing bgscan. This patch performs noise
floor calibration after the fast and full reset.

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