staging: comedi: addi-data: use attach_pci callback

Use the comedi pci auto config mechanism to attach the addi-data
drivers. This allows removing all the PCI bus walking code.

Add a function, addi_find_boardinfo(), to find the driver specific
boardinfo. Since this function is currently in the common code we
have to use the pointer to the boardinfo that is stored in the
comedi_driver pointer.

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>