mwifiex: fix AP unable to start in VHT40 problem

This patch populates secondary channel offset and downloads it to
firmware to fix the problem.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>