mwifiex: fix invalid HT IE configuration in FW

This patch fixes an issue where it was discovered that driver is setting
invalid HT IEs to FW. This was happening because bug in parsing HT IE.
Driver would incorrectly point to start of HT IE while FW only needs actual
HT configuration - excluding EID and length.

Signed-off-by: Zhaoyang Liu <liuzy@marvell.com>
Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>