staging: comedi: jr3_pci: remove devpriv->pci_dev

The `pci_dev` member of `struct jr3_pci_dev_private` is used to point to
the `struct pci_dev`.  This is redundant as the `struct comedi_device`
already has a pointer to the `struct device` within the `struct pci_dev`
and there is a convenient inline function, `comedi_to_pci_dev(dev)` that
returns a pointer to the `struct pci_dev`.

Remove the redundant `pci_dev` member and use alternate ways to get at
the `struct pci_dev`.

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