staging: comedi: daqboard2000: add back subsystem_device check

As mentioned by Ian Abbott, this driver originally checked
the pci_dev subsystem_device in order to make sure that the
pci_dev was compatible with this driver. The cleanup of the
"find pci device" code removed this check. Add it back.

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