libertas: Reduce the WPA key installation time (fixups)

This patch addresses comments from Dan Williams about the patch
committed as "libertas: Reduce the WPA key installation time."

Signed-off-by: Javier Cardona <javier@cozybit.com>
Acked-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>