staging: comedi: ni_6527: move ni6527_driver

Move the `struct comedi_driver ni6527_driver` variable further down the
function to be closer to the `module_comedi_pci_driver()` module call
and to avoid having to forward declare `ni6527_attach()` and
`ni6527_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>