staging: comedi: adl_pci6208: refactor pci6208_find_device()

Make the "find pci device" functions consistent in the comedi
drivers. Hopefully well be able to move it into the core...

Refactor the "find pci device" function to return a pointer to
the found struct pci_dev instead of an error code. Also, change
some of the tests to reduce the indent level of the code. Pass
the struct comedi_devconfig pointer to the function instead of
the bus/slot numbers.

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