staging: comedi: check comedi_auto_config() params

Do some minimal error checking of the parameters of
`comedi_auto_config()`.  Just make sure the `hardware_device` and
`driver` parameters are non-NULL.

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>