staging: comedi: Convert struct addi_board initialization to C99 format

Convert the struct addi_board initialization to C99 format and remove
all the NULL or 0 initializers. This makes maintaining and editing the
code simpler and less error prone.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>