staging: comedi: jr3_pci: remove devpriv->pci_enabled

The `pci_enabled` member of `struct jr3_pci_dev_private` is used to
indicate whether the call to `comedi_pci_enable()` was successful.  The
'detach' routine `jr3_pci_detach()` uses this to decide whether to call
`comedi_pci_disable()`.  The `iobase` member of `struct comedi_device`
is not used by this driver so it can be used for the same purpose.

Remove the `pci_enabled` member and use the spare `dev->iobase` instead.

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