staging: comedi: ni_mio_common: Allow alternate board name for routes

staging: comedi: ni_mio_common: Allow alternate board name for routes

We do not have or do not provide routing information for all supported
boards.  Some of the boards for which we do not provide routing
information actually have routes that are identical to a similar board
for which we already provide routing information.

To allow boards to share identical routing information, add an
`alt_route_name` member to `struct ni_board_struct`.  This will be
initialized to `NULL` for all boards except those that will use make use
of the identical routing information that has been provided for a
similar board, in which case it will name that board.  Pass the
`alt_route_name` member value to `ni_assign_device_routes()` as the
`alt_board_name` parameter, which it will use if no routing information
could be found for the actual board name.

Cc: Éric Piel <piel@delmic.com>
Cc: Spencer E. Olson <olsonse@umich.edu>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20200207151400.272678-4-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>