mwifiex: save and copy AP's VHT capability info correctly

While preparing association request, intersection of device's
VHT capability information and corresponding field advertised
by AP is used.

This patch fixes a couple errors while saving and copying vht_cap
and vht_oper fields from AP's beacon.

Cc: <stable@vger.kernel.org> # 3.9+
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>