mwifiex: use existing helper function mwifiex_fill_cap_info

Use existing helper function mwifiex_fill_cap_info to fill
the HT CAP info for ibss beacons.

Also removing extra parenthesis block for better readability.

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>