mwifiex: update MCS information as per antenna settings

Even if the device is changed to 1X1 mode, data is sent with
higher MCS rates after association.

This patch fixes the problem by updating MCS information field
in HT capability when antenna setting changes so that correct
information will be advertised in association and probe request.

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>