mwifiex: cleanup VHT cap

Firmware returned VHT cap has the same format that cfg80211
expects. There is no need to parse the vht cap from the firmware
and then set it to ieee80211_sta_vht_cap. Just copying is
sufficient.

Signed-off-by: Yogesh Ashok Powar <yogeshp@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>