mwifiex: use correct htcapinfo for HT20 ibss network

It is observed that same htcapinfo ie is included in beacon for
HT20, HT40+ and HT40- ibss networks. This patch makes sure that
we will not advertise 40Mhz flags while creating/joining ibss
network in HT20 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>