mwifiex: handle auto authentication mode correctly

When authentication type is configured to NL80211_AUTHTYPE_AUTOMATIC,
driver tries to connect using open mode. The association is failed
if AP is configured in shared mode.

This patch adds code to try association using shared mode as well if
open mode association fails.

Now since we returned exact error code in association response handler
(instead of -1), corresponding changes are done in
mwifiex_process_cmdresp().

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>