staging: comedi: dt3000: cleanup "find pci device" code

The "find pci device" code for this driver was split between
two functions which could cause the driver to walk the pci
bus multiple times while looking for a match.

Consolidate the functions into the format that is more
standard for the comedi pci drivers.

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>