[PATCH] bogus BUILD_BUG_ON() in bpa_iommu

BUILD_BUG_ON(1) is asking for trouble (and getting it) when used in that
manner - dead code elimination happens after we parse it and invalid
type is invalid type, dead code or not.

It might be version-dependent, but at least 4.0.1 refuses to accept
that.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>