USB: opticon: fix DMA from stack

Make sure to allocate the control-message buffer dynamically as some
platforms cannot do DMA from stack.

Note that only the first byte of the old buffer was used.

Cc: <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>