BUILD_BUG_ON_ZERO: fix sparse breakage

BUILD_BUG_ON_ZERO and BUILD_BUG_ON_NULL must return values, even in the
CHECKER case otherwise various users of it become syntactically invalid.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>