staging: comedi: me4000: move struct me4000_board definition

Move the struct me4000_board definition from the header to the c file.
It's not used by any other source.

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>