staging: vt6656: use off stack for out buffer USB transfers.

Since 4.9 mandated USB buffers be heap allocated this causes the driver
to fail.

Since there is a wide range of buffer sizes use kmemdup to create
allocated buffer.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Cc: <stable@vger.kernel.org> # v4.9+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>