staging: comedi: das08: Avoid zero initializers in board structure

Don't bother initializing the `i8255_offset` and/or `i8254_offset`
members of `struct das08_board_struct` in `das08_boards[]` and
`das08_cs_boards[]` if they are zero as they are implicitly initialized
to zero anyway, and zero means the corresponding subdevices are absent.

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