staging: wfx: simplify wfx_config()

Now that wfx_config() only handles IEEE80211_CONF_CHANGE_PS, it can be
simplified.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200115135338.14374-16-Jerome.Pouiller@silabs.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>