staging: comedi: das08: absorb das08_pci_attach_common()

Absorb `das08_pci_attach_common()` into `das08_attach_pci()` since
that's the only place it was called from.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>