ath9k: Properly use unlikely check macro

AUTOSLEEP feature is enabled only for AR9271 and AR9003 version
chipsets.So unlikely macro should be used only to check whether
auto-sleep feature is enabled

Signed-off-by: Mohammed Shafi Shajakhan <mshajakhan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>