staging: wlan-ng: replace kmalloc and memset with kzalloc

Replace kmalloc and memset with a single call of kzalloc in
file of wlan-ng.

Signed-off-by: Tapasweni Pathak <tapaswenipathak@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>