ath9k: invalidate all calibrations at once

Previously after the calibration validity period is over,
calibrations are invalidated in a one at time manner. So, for AR9002
family, which has three calibrations, the full recalibration interval
becomes 3 x ATH_RESTART_CALINTERVAL. And each next calibration will be
separated by the ATH_RESTART_CALINTERVAL time from a previous one.

It seems like it is better to do whole recalibration at once. Also, this
change makes the driver behaviour a little simpler. So, invalidate all
calibrations at once at the end of the calibration validity interval.

This change affects only AR9002 chips family, since the AR9003 utilize
only a single calibration.

Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200424004923.17129-6-ryazanov.s.a@gmail.com