LU-9859 mdt: replace CLASSERT with BUILD_BUG_ON

LU-9859 mdt: replace CLASSERT with BUILD_BUG_ON

Replace the lustre specific CLASSERT in mdt layer with what the
linux kernel provides. Note the logic is reverse.

Test-Parameters: trivial

Change-Id: I1e4d75a6643204c55c888a5c2e95a8b12251f5b7
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-on: https://review.whamcloud.com/32219
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Ben Evans <bevans@cray.com>
Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Oleg Drokin <green@whamcloud.com>