[PATCH] DocBook: allow even longer return types

kernel-doc errored out because it could not understand the new __copy_to_user
definition.  Now we allow return types with four words.

Signed-off-by: Martin Waitz <tali@admingilde.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>