p54: disable PS by default

Johannes kindly pointed out that I completely missed a hunk in
his patch: "[PATCH] cfg80211: allow driver to override PS default".

The driver must explicitly set ps_default to false,
as the setting is pre-filled with the kconfig default.

Signed-off-by: Christian Lamparter <chunkeey@web.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>