ath9k: fix suspend by waking device prior to stop

Ensure the device is awake prior to trying to tell hardware
to stop it. Impact of not doing this is we can likely leave
the device in an undefined state likely causing issues with
suspend and resume. This patch ensures harware is where it
should be prior to suspend.

Cc: stable@kernel.org
Signed-off-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>