staging: vt6656: sparse fixes: iwctl_siwgenie use memcpy.

extra is in kernel space replace copy_from_user with
memcpy with no need to error check.

We already know that extra is valid by error checking
on wrq->length.

sparse warning
iwctl.c:1567:53: warning: incorrect type in argument 2 (different address spaces)
iwctl.c:1567:53:    expected void const [noderef] <asn:1>*from
iwctl.c:1567:53:    got char *extra

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>