staging: comedi: ni_atmio: cleanup ni_getboardtype()

Make this function return a pointer to the boardinfo instead of an index.

For aesthetics, rename the function to ni_atmio_probe().

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