ath9k_htc: Fix suspend/resume

The HW has to be set to FULLSLEEP mode during suspend,
when no interface has been brought up. Not doing this would
break resume, as the chip won't be powered up at all.

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