staging: comedi: amplc_dio200: rename struct dio200_layout_struct

Now that the tag name `dio200_layout` is available, rename `struct
dio200_layout_struct` to `struct dio200_layout` as the `_struct` suffix
is a bit redundant and I plan to use this type in other places in the
module.

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