staging: comedi: adl_pci9111: remove pci9111_board_nbr macro

This macro is an open-coded version of the kernels ARRAY_SIZE
macro. Use the kernel provided macro instead.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>