staging:wlan-ng: use memdup_user instead of kmalloc/copy_from_user

memdup_user() is shorter and safer equivalent
of kmalloc/copy_from_user pair.

Signed-off-by: Ivan Safonov <insafonov@gmail.com>
Link: https://lore.kernel.org/r/20210213120527.451531-1-insafonov@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>