staging: comedi: ni_65xx: move ni_65xx_driver

Move the `struct comedi_driver ni_65xx_driver` variable further down the
function to be closer to the `module_comedi_pci_driver()` module call
and to avoid having to forward declare `ni_65xx_attach()` and
`ni_65xx_detach()`.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>