staging: comedi: jr3_pci: replace devpriv->iobase with dev->mmio

The "jr3_pci" driver currently uses the `iobase` member of its private
device data `struct jr3_pci_dev_private` to store a pointer to its
ioremapped register region.  Use the `mmio` member of the `struct
comedi_device` to store this instead, and remove the `iobase` member.
The `iobase` member was of type `struct jr3_t __iomem *`, with the
board's complicated register layout described by `struct jr3_t`.  The
`mmio` member is a generic `void __iomem *`, so its value needs
converting to a `struct jr3_t __iomem *` for our purposes.

Change the clean-up in `jr3_pci_detach()` to call `comedi_pci_detach()`
instead of `comedi_pci_disable()`, as that will iounmap `dev->mmio` for
us.

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