staging: comedi: adl_pci7296: factor out the PCI device code

Factor out the code that finds a matching PCI device from attach
function. This allows reducing the indent level of the remaining
code in the attach function.

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