mwifiex: change return types to void

Functions mwifiex_11n_dispatch_pkt_until_start_win and
mwifiex_11n_scan_and_dispatch used to always return value
zero for all inputs. Changing these functions to void.

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>