mwifiex: fix WPA connection problem

Device fails to connect to some AP's configured in WPA
security mode. Currently IE buffer parsing logic in driver
expects WPA IE to be present at the beginning of IE buffer.
Otherwise connection is failed with 'incompatible network
setting' error.

This patch fixes the problem by improving IE buffer parsing
logic.

Signed-off-by: chunfan chen <jeffc@marvell.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>