staging: comedi: addi_apci_1564: remove use of devpriv->iobase

devpriv->iobase is currently being used to hold the iobase address used to
read/write the board's registers.  The same address is stored in the
comedi_device dev->iobase.  We use that instead.  The eventual goal is to
decrease the driver's use of the struct addi_private, so that it may
eventually use a much slimmer specialized private struct instead, as the
other addi_apci_* drivers do.

Signed-off-by: Chase Southwood <chase.southwood@yahoo.com>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>