libertas: Set/clear WPA keys before the WEP ones

With the v10 firmware running on 8688 HW, clearing WPA keys after setting the
WEP key prevents us from being able to associate with WEP APs.
Swapping the calling order for assoc_helper_wpa_keys() and
assoc_helper_wep_keys fixes that issue.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>