ath9k: set ps_default as false

Copied from original one-line patch here:

	http://bugzilla.kernel.org/show_bug.cgi?id=14267#c26

(This is for 2.6.33 and beyond, where the bool was changed to a flag by
"cfg80211: convert bools into flags". -- JWL)

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