[ath_hal] Return failure if noise floor calibration fails.
If we fail noise floor calibration then we may end up with a deaf NIC
which we can't recover without a full chip reset.
Earlier chips seem to get less stuck in this condition versus AR9280/later
and AR9300/later, but whilst here just fix up the AR5212 era chips to also
return NF calibration failures.
This HAL routine would only return failure if the channel was not configured.
This is a no-op until the driver side code for doing resets and the HAL
code for being told about the reset type (and then handling it!) is
- AR9280, STA mode
- AR2425, STA mode
- AR9380, STA mode