mwifiex: enable HT operating mode

This patch sets default adapter channel_type as HT. Hence the device
will opearate in HT mode.

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>