staging: comedi: me4000: remove ME4000_BOARD_VERSIONS

Remove the terminating entry in the boardinfo so that ARRAY_SIZE
works correctly. Then remove ME4000_BOARD_VERSIONS and just use
ARRAY_SIZE in the probe.

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>