staging: comedi: addi_apci_3501: remove dependency on addi_common.h

Create a struct to hold the private data still used by this driver.
This removes the last dependencies on the addi-data "common" code
so we can also remove the #include of addi_common.h.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>