staging: comedi: remove unneeded settings of `dev->iobase`

Some PCI drivers use the "spare" `iobase` member of `struct
comedi_device` as a flag to indicate that the call to
`comedi_pci_enable()` was successful.  This is no longer necessary now
that `comedi_pci_enable()` and `comedi_pci_disable()` use the
`ioenabled` member of `struct comedi_device` themselves to keep track of
what needs to be done.

Remove the unnecessary assignments to the `iobase` member in the
relevant drivers.

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