ath9k: Do not try to calibrate radio when in sleep mode

When the chip is in sleep mode, there is no point trying to calibrate
the radio since it will just results in incorrect values being read
from registers and other potential issues. In addition, if we actually
start processing calibrate, do not allow the chip to be put into sleep
until we have completed the calibration step.

Signed-off-by: Jouni Malinen <jouni.malinen@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>