cfg80211: Fix WEXT compat siwauth wpa and group cipher

Neither of these commands should clear the current configuration value
if they return error. Furthermore, cfg80211_set_cipher_group() should
be able to handle IW_AUTH_CIPHER_NONE without reporting error.

Signed-off-by: Jouni Malinen <j@w1.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>