staging: comedi: das08: Remove pc104 bustype value

Remove the `pc104` value from `enum das08_bustype` and replace
occurrences of it in the code and data with the `isa` value.  The code
treats them as equivalent anyway with expressions like
`(thisboard->bustype == isa || thisboard->bustype == pc104)`.

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